CVE-2025-48946: 
NixOS vulnerability analysis and mitigation

CVE-2025-48946 affects liboqs, a C-language cryptographic library that implements post-quantum cryptography algorithms. The vulnerability was discovered in versions prior to 0.13.0, specifically related to the HQC (Hamming Quasi-Cyclic) algorithm implementation. Disclosed on May 30, 2025, the issue involves a theoretical design flaw in the HQC algorithm that leads to large numbers of malformed ciphertexts sharing the same implicit rejection value (GitHub Advisory).

The vulnerability stems from a design flaw in how HQC implements the Fujisaki-Okamoto (FO) transform, particularly in its handling of the 'salt' component in the ciphertext. The issue allows for a two-query decryption failure oracle where an attacker can determine if decryption failed by comparing decapsulation results of two ciphertexts that differ only in their salt values. The CVSS v3.1 score is 3.7 (Low) with vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N (Wiz, GitHub Advisory).

While no concrete attack on the algorithm is currently known, the vulnerability affects the security guarantees of HQC, particularly in protocols involving key derivation. The flaw means that HQC does not provide the same security guarantees as other post-quantum algorithms like Kyber or ML-KEM. Users must take extra care when implementing the algorithm in cryptographic protocols (GitHub Advisory, Durum Blog).

As a mitigation measure, HQC has been disabled by default in liboqs starting from version 0.13.0. There is currently no patch available in liboqs, and the Open Quantum Safe team will update their implementation after the HQC team releases an updated algorithm specification. Users are advised to disable the HQC algorithm family until a fix is available (GitHub Commit, GitHub Advisory).

The vulnerability was initially reported by Markku-Juhani O. Saarinen to the NIST pqc-forum mailing list, leading to technical discussions among cryptography experts. The HQC team has acknowledged the issue and indicated they are working on modifications to address the vulnerability (PQC Forum).