CVE-2025-48946 identifies a cryptographic vulnerability in the open-quantum-safe project's liboqs library, specifically affecting versions prior to 0.13.0. liboqs is a C-language library designed to provide implementations of post-quantum cryptography algorithms, which are intended to be secure against attacks from quantum computers. The vulnerability concerns the HQC (Hamming Quasi-Cyclic) algorithm, which has a theoretical design flaw leading to a large number of malformed ciphertexts sharing the same implicit rejection value. This flaw means that the algorithm does not provide the expected level of security guarantees, particularly in protocols involving key derivation. Although no concrete attacks exploiting this flaw are currently known, the weakness implies that HQC's security assurances are weaker than those of other algorithms like Kyber or ML-KEM, which are also implemented in liboqs. Due to this, HQC has been disabled by default starting with liboqs version 0.13.0, pending an updated algorithm specification from the HQC team. The vulnerability is classified under CWE-327, which relates to the use of broken or risky cryptographic algorithms. The CVSS v3.1 score is 3.7 (low severity), reflecting the low likelihood of exploitation and limited impact on confidentiality, integrity, and availability. No patches are currently available, and no known exploits exist in the wild. Users of liboqs are advised to avoid using the HQC algorithm in security-critical applications, especially those involving key derivation, until a secure update is released.

For European organizations, the impact of this vulnerability is currently limited but should not be ignored. Organizations experimenting with or deploying post-quantum cryptography solutions using liboqs versions prior to 0.13.0 and specifically enabling the HQC algorithm may face risks related to weakened cryptographic assurances. This could potentially lead to subtle cryptographic failures or reduced resistance to future cryptanalysis, undermining the confidentiality of sensitive communications or key material. However, since no active exploits or practical attacks are known, immediate risk is low. The main concern is for organizations involved in research, development, or early adoption of post-quantum cryptographic protocols, such as governmental agencies, financial institutions, and critical infrastructure operators who prioritize quantum-resistant security. The flaw could delay the secure deployment of post-quantum cryptography, impacting long-term cryptographic agility strategies. Given the growing interest in quantum-safe cryptography in Europe, especially within the EU's cybersecurity initiatives, this vulnerability highlights the importance of cautious algorithm selection and staying current with library updates.

European organizations should take the following specific actions: 1) Immediately audit their cryptographic libraries and protocols to identify any use of liboqs versions prior to 0.13.0 and check if the HQC algorithm is enabled. 2) Disable the HQC algorithm in all deployments until a secure update or revised algorithm specification is released by the HQC team. 3) Prefer alternative post-quantum algorithms with stronger security guarantees such as Kyber or ML-KEM, which are supported by liboqs and do not exhibit this flaw. 4) Monitor the open-quantum-safe project and HQC team communications for updates and patches, planning timely upgrades to liboqs 0.13.0 or later. 5) For organizations developing custom protocols, conduct thorough cryptographic reviews to avoid relying on HQC for key derivation or other critical operations. 6) Engage with cryptographic experts to assess the impact of this vulnerability on ongoing quantum-safe initiatives and adjust risk management accordingly. 7) Incorporate this vulnerability into supply chain risk assessments, ensuring third-party vendors are not using vulnerable versions of liboqs with HQC enabled.