CVE-2026-87735 in mirage-crypto-pk
Summary
by MITRE • 09/09/2026
An issue was discovered in the mirage-crypto-pk package before 2.3.0 for OCaml. There is an undocumented exception for a small message during RSA decryption or encryption.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified within the mirage-crypto-pk library, specifically affecting versions prior to 2.3.0 for the OCaml programming language, represents a critical flaw in the implementation of RSA cryptographic operations. This security issue stems from an undocumented exception that is triggered when processing small messages during either encryption or decryption phases. In standard RSA implementations, the mathematical operation involves modular exponentiation where the message size must typically be less than the modulus but often requires padding schemes such as PKCS#1 v1.5 or OAEP to ensure semantic security and prevent various attacks like chosen ciphertext attacks. The presence of an undocumented exception suggests that the library fails to handle edge cases involving small plaintext values correctly, potentially leading to unexpected control flow changes or error states rather than secure processing or explicit rejection with appropriate logging.
From a technical perspective, this flaw aligns closely with CWE-754: Improper Check for Unusual or Exceptional Conditions and CWE-209: Generation of Error Message Containing Sensitive Information if the exception reveals internal state details to an attacker. When a small message is submitted, instead of being properly padded and processed according to cryptographic standards, the library throws an exception that was not documented in its public API contract. This lack of documentation means developers integrating this library cannot anticipate or handle these specific error conditions gracefully. In many software architectures, unhandled exceptions can lead to denial of service scenarios where the application crashes or enters a degraded state, effectively disrupting availability services provided by applications relying on mirage-crypto-pk for secure communications.
The operational impact of this vulnerability is significant because it undermines both confidentiality and integrity assurances expected from RSA operations. If an attacker can trigger these exceptions repeatedly through crafted inputs containing small messages, they may induce denial-of-service conditions against systems dependent on the library. Furthermore, depending on how the exception propagates or what stack traces are exposed to end-users or logs, there is a risk of information leakage regarding internal implementation details which could aid in further exploitation attempts. The absence of proper error handling also means that applications might behave unpredictably, potentially bypassing security checks if exceptions cause early returns without completing necessary validation steps.
This issue maps directly to MITRE ATT&CK technique T1498: Network Denial of Service under the Impact tactic, as triggering unhandled exceptions can crash services or degrade performance significantly. It also relates to CWE-20 which covers input validation failures since the library does not adequately validate message sizes before processing them through RSA algorithms. The root cause lies in insufficient defensive programming practices within the cryptographic module where edge cases are not explicitly handled with secure defaults rather than relying on implicit runtime exceptions that may expose system instability.
To mitigate this vulnerability, organizations using mirage-crypto-pk must upgrade to version 2.3.0 or later which addresses these undocumented exception behaviors by implementing robust input validation and consistent error handling mechanisms. Developers should ensure that all cryptographic operations include explicit checks for message size constraints before invoking encryption or decryption functions. Additionally, integrating comprehensive logging frameworks can help detect attempts to exploit this flaw in production environments while maintaining audit trails for forensic analysis if incidents occur. Regular security assessments of third-party dependencies are essential to identify such subtle implementation flaws early in the development lifecycle and prevent their deployment into critical infrastructure components relying on strong cryptographic guarantees.