Skip to content

Brillig: Heap corruption in foreign call results with nested tuple arrays

Critical severity GitHub Reviewed Published Apr 14, 2026 in noir-lang/noir • Updated Apr 27, 2026

Package

cargo brillig (Rust)

Affected versions

<= 1.0.0-beta.18

Patched versions

1.0.0-beta.19

Description

Description

Noir programs can invoke external functions through foreign calls. When compiling to Brillig bytecode, the SSA instructions are processed block-by-block in BrilligBlock::compile_block(). When the compiler encounters an Instruction::Call with a Value::ForeignFunction target, it invokes codegen_call() in brillig_call/code_gen_call.rs, which dispatches to convert_ssa_foreign_call().

Before emitting the foreign call opcode, the compiler must pre-allocate memory for any array results the call will return. This happens through allocate_external_call_results(), which iterates over the result types. For Type::Array results, it delegates to allocate_foreign_call_result_array() to recursively allocate memory on the heap for nested arrays.

The BrilligArray struct is the internal representation of a Noir array in Brillig IR. Its size field represents the semi-flattened size, the total number of memory slots the array occupies, accounting for the fact that composite types like tuples consume multiple slots per element. This size is computed by compute_array_length() in brillig_block_variables.rs:

pub(crate) fn compute_array_length(item_typ: &CompositeType, elem_count: usize) -> usize {
    item_typ.len() * elem_count
}

For the outer array, allocate_external_call_results() correctly uses define_variable(), which internally calls allocate_value_with_type(). This function applies the formula above, producing the correct semi-flattened size.

However, for nested arrays, allocate_foreign_call_result_array() contains a bug. When it encounters a nested Type::Array(types, nested_size), it calls:

Type::Array(_, nested_size) => { 
	let inner_array = self.brillig_context.allocate_brillig_array(*nested_size as usize);
	// ....
}

The pattern Type::Array(_, nested_size) discards the inner types with _ and uses only nested_size, the semantic length of the nested array (the number of logical elements), not the semi-flattened size. For simple element types this works correctly, but for composite element types it under-allocates. Consider a nested array of type [(u32, u32); 3]:

  • Semantic length: 3 (three tuples)
  • Element size: 2 (each tuple has two fields)
  • Required semi-flattened size: 6 memory slots

The current code passes 3 to allocate_brillig_array(), which then calls codegen_initialize_array(). This function allocates array.size + ARRAY_META_COUNT slots, only 4 slots instead of the required 7 (6 data + 1 metadata). When the VM executes the foreign call and writes 6 values plus metadata, it overwrites adjacent heap memory.

Impact

Foreign calls returning nested arrays of tuples or other composite types corrupt the Brillig VM heap.

Recommendation

Multiply the semantic length by the number of element types when allocating nested arrays. Extract the inner types from the pattern and replace the nested_size argument to allocate_brillig_array() with types.len() * nested_size to compute the semi-flattened size. Alternatively, reuse the existing compute_array_length() helper function to maintain consistency with outer array allocation.

References

@Savio-Sou Savio-Sou published to noir-lang/noir Apr 14, 2026
Published to the GitHub Advisory Database Apr 21, 2026
Reviewed Apr 21, 2026
Published by the National Vulnerability Database Apr 23, 2026
Last updated Apr 27, 2026

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(6th percentile)

Weaknesses

Incorrect Calculation of Buffer Size

The product does not correctly calculate the size to be used when allocating a buffer, which could lead to a buffer overflow. Learn more on MITRE.

CVE ID

CVE-2026-41197

GHSA ID

GHSA-jj7c-x25r-r8r3

Source code

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.
⚡