Detection Guidance

Detection of this vulnerability involves verifying whether the vulnerable version of the CROSS implementation is in use, specifically checking if the `crypto_sign_open()` function lacks the security check introduced in commit fc6b7e7.

One practical approach is to inspect the source code or binary for the presence of the validation that ensures the input signature length (`smlen`) is at least the size of the `CROSS_sig_t` structure. If this check is missing, the system is vulnerable.

Since this is a code-level vulnerability, network detection commands are not directly applicable. However, you can use the following commands to check the version or patch status if you have access to the source or binaries:

• Use `git log -p -1 fc6b7e7` in the CROSS implementation repository to verify if the patch commit is applied.
• Search the source code for the presence of the length check in `Reference_Implementation/lib/sign.c` using `grep -A5 'crypto_sign_open' Reference_Implementation/lib/sign.c` and look for the validation of `smlen`.
• If binaries are used, check their build date or version metadata to confirm if they include the patch.

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Mitigation Strategies

The immediate mitigation step is to apply the patch introduced in commit fc6b7e7 to the CROSS implementation. This patch adds a validation in the `crypto_sign_open()` function to prevent buffer overflow by rejecting undersized signatures.

If you maintain or deploy the CROSS implementation, update your codebase or binaries to include this fix as soon as possible.

Additionally, avoid processing untrusted or malformed signatures that could trigger the buffer overflow.

Monitor for any updates or advisories from the CROSS implementation maintainers and apply further patches or security recommendations promptly.

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Executive Summary

CVE-2026-41509 is a vulnerability in the CROSS implementation of the CROSS post-quantum signature algorithm. It involves a buffer overflow in the function crypto_sign_open() caused by an integer underflow of the variable mlen. This underflow leads to memory corruption, which can cause the program to behave unexpectedly or crash. The issue arises because the function does not properly validate the length of the input signature before processing it.

The vulnerability was fixed by adding a security check in the crypto_sign_open() function to ensure that the input signature length (smlen) is at least as large as the expected signature structure size. If the input is smaller, the function returns an error immediately, preventing the buffer overflow.

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Impact Analysis

This vulnerability can lead to memory corruption through a stack-based or heap-based buffer overflow. Such memory corruption can allow an attacker to execute arbitrary code or cause a denial of service by crashing the application using the vulnerable function.

Because the flaw is in the implementation of the signature verification function, an attacker might exploit it by providing specially crafted signatures that trigger the buffer overflow, potentially compromising the security of systems relying on this implementation.

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Compliance Impact

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

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