The vulnerability identified as CVE-2026-24785 concerns the jmlepisto clatter library, a Rust implementation of the Noise protocol framework designed for no_std environments and supporting post-quantum cryptography. Prior to version 2.2.0, clatter allowed the use of post-quantum handshake patterns that violated the pre-shared key (PSK) validity rule defined in Section 9.3 of the Noise Protocol Framework specification. Specifically, the affected patterns (e.g., noise_pqkk_psk0, noise_pqkn_psk0, noise_pqnk_psk0, noise_pqnn_psk0, and some hybrid variants) permitted PSK-derived keys to be used for encryption without the necessary randomization through self-chosen ephemeral randomness. This omission undermines the security guarantees of the handshake by enabling potential catastrophic key reuse, which can lead to the compromise of confidentiality and integrity of the encrypted communication channel. The flaw is rooted in the use of a broken or risky cryptographic algorithm approach (CWE-327), where the cryptographic protocol does not enforce proper randomness in key derivation. The vulnerability has a CVSS 4.0 base score of 8.0, indicating high severity, with network attack vector, no required privileges or user interaction, and high impact on confidentiality and integrity. The issue has been fully addressed in clatter version 2.2.0, which introduces runtime checks to detect and prevent the use of offending handshake patterns. Users are advised to upgrade to this version or avoid using the vulnerable *_psk0 post-quantum handshake variants. Custom handshake patterns should be carefully reviewed to ensure compliance with the PSK validity rule and proper ephemeral randomness usage.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on the clatter library for secure communications in embedded or constrained environments where no_std Rust libraries are preferred. The weakened cryptographic guarantees can lead to exposure of sensitive data, interception, or manipulation of communications, undermining confidentiality and integrity. This is particularly critical for sectors handling sensitive personal data under GDPR, such as finance, healthcare, and government services. The potential for catastrophic key reuse increases the risk of long-term compromise of encrypted sessions, which could facilitate espionage, data breaches, or disruption of critical services. Organizations using affected versions of clatter in IoT devices, secure messaging, or post-quantum cryptographic applications may face increased risk of targeted attacks. Although no exploits are currently known in the wild, the high CVSS score and nature of the vulnerability warrant proactive mitigation to prevent future exploitation.

European organizations should immediately upgrade any deployments of the jmlepisto clatter library to version 2.2.0 or later, which contains the necessary runtime checks and fixes. If upgrading is not immediately feasible, avoid using any post-quantum handshake patterns with the *_psk0 suffix, as these are known to violate the PSK validity rule. Conduct a thorough audit of all custom handshake patterns to ensure they comply with the Noise Protocol Framework's PSK validity requirements and enforce proper ephemeral randomness. Implement monitoring to detect anomalous cryptographic behavior or unexpected key reuse patterns. For embedded and constrained environments, validate that cryptographic libraries are up to date and that secure coding practices are followed to prevent misuse of cryptographic primitives. Engage with vendors and suppliers to confirm that their products using clatter have applied the patch. Finally, consider incorporating cryptographic protocol fuzzing and formal verification tools to detect similar protocol compliance issues in future development.