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ConnectBot SSH Client Library: Excessive allocation and integer overflow in DER private-key parsing

Moderate severity GitHub Reviewed Published Jun 11, 2026 in connectbot/cbssh • Updated Jun 12, 2026

Package

maven org.connectbot.sshlib:sshlib (Maven)

Affected versions

<= 0.3.0

Patched versions

None

Description

Summary

The DER parser used for application-supplied private keys did not safely validate encoded length values before converting them to Int values or allocating arrays.

A malformed private-key file could encode a length that overflowed or wrapped around, or request an allocation much larger than the available input. This could cause parsing errors or an uncaught OutOfMemoryError, potentially terminating the application process.

Details

The issue was in DerReader.readLength() and primitive readers such as readInteger().

readLength() previously accepted up to 127 length octets and accumulated them into an Int:

length = (length shl 8) or nextByte

This permitted integer overflow. For example:

  • 0x1_0000_0001 wrapped to 1.
  • 0x8000_0000 wrapped to Int.MIN_VALUE.

Primitive readers then allocated memory based on the resulting value without first checking it against the remaining input:

val bytes = ByteArray(length)
data.get(bytes)

A six-byte DER value declaring a 1 GiB INTEGER caused an immediate OutOfMemoryError when tested with a constrained JVM heap. Because OutOfMemoryError is not an Exception, it is not caught by the public-key authentication error handling and may terminate the application process.

A zero-length DER INTEGER is also invalid, but it does not produce BigInteger.ZERO: Java throws NumberFormatException when constructing a BigInteger from an empty byte array. No weakened or usable cryptographic key has been demonstrated through this issue.

Attack Requirements

The affected DER parser processes private-key material explicitly supplied by the application through APIs such as:

  • SshClient.authenticatePublicKey()
  • SshKeys.decodePemPrivateKey()
  • SshSigning.sign()
  • SshSigning.getPublicKey()

The DER input is not populated from SSH server host keys or agent-forwarding requests. Exploitation therefore requires a user or application to load an attacker-provided private-key file. The issue is not remotely exploitable by an SSH server.

Impact

Successful exploitation can cause:

  • Incorrect DER length interpretation due to integer wraparound
  • Excessive memory allocation
  • An uncaught OutOfMemoryError
  • Loss of availability of the affected application process

There is no demonstrated confidentiality or integrity impact.

Remediation

The DER parser now:

  • Rejects indefinite lengths
  • Explicitly limits long-form lengths to Int.SIZE_BYTES (four octets) and rejects values above Int.MAX_VALUE
  • Accumulates long-form lengths in a Long before converting to Int
  • Rejects truncated and non-minimal length encodings
  • Checks declared lengths against the remaining input before allocation or advancing the input position
  • Rejects zero-length DER INTEGER, BIT STRING, and OBJECT IDENTIFIER values where an empty encoding is invalid
  • Rejects non-canonical DER INTEGER encodings with redundant sign octets

The bounds checks are implemented in shared DER reader helpers and apply to INTEGER, OCTET STRING, BIT STRING, OBJECT IDENTIFIER, SEQUENCE, context-specific values, and skipped values. PKCS#1 RSA and SEC1 EC private keys pass application-supplied DER directly through these helpers. PKCS#8 input is parsed by the JCA provider, and OpenSSH private keys use a separate wire-format parser rather than DerReader.

References

@kruton kruton published to connectbot/cbssh Jun 11, 2026
Published to the GitHub Advisory Database Jun 12, 2026
Reviewed Jun 12, 2026
Last updated Jun 12, 2026

Severity

Moderate

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 Local
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction Active
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
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:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Integer Overflow or Wraparound

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number. Learn more on MITRE.

Memory Allocation with Excessive Size Value

The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-vc8p-8pxg-rfwg

Source code

Credits

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