ML-KEM NEON Ciphertext Comparison Flaw Weakens IND-CCA2 Security

Executive Summary

This vulnerability involves the ML-KEM ARM64 NEON ciphertext comparison process, which only compares half of the input ciphertext. This flaw breaks the Fujisaki-Okamoto transform's implicit rejection mechanism, weakening the IND-CCA2 security on that code path.

Because the constant-time comparison ignores part of the re-encrypted ciphertext, a decapsulating party might fail to detect a manipulated ciphertext and proceed without performing the required implicit rejection.

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Impact Analysis

This vulnerability can allow an attacker to manipulate ciphertexts without detection during the decapsulation process. As a result, the security guarantees of the cryptographic scheme are weakened, potentially allowing unauthorized access or data compromise due to the failure to reject invalid ciphertexts.

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Compliance Impact

The vulnerability weakens the IND-CCA2 security of the ML-KEM ARM64 NEON ciphertext comparison by failing to detect manipulated ciphertexts due to incomplete comparison. This failure to perform the standard's required implicit rejection could lead to cryptographic weaknesses.

While the CVE description does not explicitly mention compliance with standards such as GDPR or HIPAA, weakened cryptographic security can potentially impact compliance with these regulations, which require strong data protection measures.

Therefore, this vulnerability may indirectly affect compliance by undermining the security guarantees expected under such standards, but no direct linkage or specific compliance impact is detailed in the provided information.

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Mitigation Strategies

To mitigate this vulnerability, update the wolfSSL library to a version that includes the fix for the ML-KEM NEON compare logic on AArch64. The fix corrects the ciphertext comparison to properly enforce the Fujisaki-Okamoto transform's implicit rejection, preventing manipulated ciphertext from bypassing security checks.

Applying the patch from wolfSSL's Pull Request #10192 or upgrading to a version containing these changes is recommended to ensure robust security against this issue.

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