Executive Summary

CVE-2026-44518 is an out-of-bounds read vulnerability in the liboqs cryptographic library, specifically in the XMSS and XMSS^MT stateful signature verification code. The issue arises when the verification function is called with a signature buffer that is shorter than expected for the given parameter set. The implementation does not properly validate the length of the signature buffer and proceeds to read beyond its end.

Although the out-of-bounds bytes are only used internally for hash computation and are not exposed to the caller or attacker, this improper memory access can cause the verifying process to crash if it reads into unmapped memory.

The vulnerability was fixed in liboqs version 0.16.0 by adding explicit length validation at the verification entry points to reject undersized signatures before any memory access occurs.

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Compliance Impact

The provided information does not specify any direct impact of the CVE-2026-44518 vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Impact Analysis

The primary impact of this vulnerability is a potential denial of service (DoS) caused by a crash of the verifying process. This happens if the out-of-bounds read crosses into an unmapped memory page.

Since the out-of-bounds data is not returned or exposed to an attacker, there is no direct information leak or compromise of confidentiality or integrity.

However, the crash could disrupt services relying on liboqs for signature verification, potentially affecting availability.

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Detection Guidance

This vulnerability manifests as a possible crash (denial of service) in the verifying process when the signature verification function reads beyond the end of a buffer. Detection can involve monitoring for crashes or abnormal termination of processes using liboqs versions prior to 0.16.0, especially those performing XMSS or XMSS^MT signature verification.

Since the issue is triggered by signature buffers shorter than expected, one detection approach is to audit or log signature verification calls to check for undersized signature buffers.

No specific commands are provided in the resources, but general steps could include:

• Check the version of liboqs in use to identify if it is older than 0.16.0.
• Monitor application logs or system logs for crashes or segmentation faults related to signature verification processes.
• Use debugging tools (e.g., gdb) to trace crashes in the verification function to confirm out-of-bounds reads.
• If source code or binaries are available, verify if the signature length validation is implemented as per the fix.

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Mitigation Strategies

The primary immediate mitigation step is to upgrade liboqs to version 0.16.0 or later, where the vulnerability has been fixed by adding explicit signature length validation.

If upgrading is not immediately possible, ensure that any inputs to the XMSS or XMSS^MT signature verification functions are validated externally to confirm that signature buffers meet the expected size requirements before verification.

Additionally, monitor the verifying processes for crashes and consider implementing process supervision or restart mechanisms to reduce denial of service impact.

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