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The vulnerability (CVE-2026-XXXXX) is a protocol compliance flaw within the Clatter library’s implementation of the Noise Protocol Framework. It incorrectly permits the use of Pre-Shared Keys (PSKs) in specific post-quantum and hybrid handshake patterns—namely `_psk0` variants—that violate Section 9.3 of the Noise specification. This rule mandates that a PSK must be randomized by ephemeral randomness contributed by both parties to ensure key independence. In the affected patterns, the handshake messages could be structured such that the PSK-derived symmetric key is used for encryption before the initiator’s ephemeral public key is mixed into the key chain. This sequence breaks the cryptographic guarantee that each session key is unique and properly randomized. Consequently, if an attacker observes multiple handshakes using the same PSK, they could potentially perform key reuse attacks, leading to a catastrophic loss of confidentiality where encrypted messages might be decrypted or manipulated. The flaw resides in the pattern definition logic, which failed to enforce the necessary ordering of crypto operations, allowing these insecure handshake sequences to proceed without runtime validation.
Platform: Clatter
Version: < v2.2.0
Vulnerability : PSK Rule Violation
Severity: High
date: Jan 27-28 2026
Prediction: Patched v2.2.0
What Undercode Say:
Check current Clatter version clatter --version Scan code for vulnerable pattern usage grep -r "noise_pq[k,n][k,n]_psk0" ./src/ Update to patched version cargo update clatter
How Exploit:
An attacker could passively capture multiple handshake sessions using a compromised or brute-forced weak PSK. By analyzing the non-conforming message flow where the PSK is used before full ephemeral randomness is incorporated, they could leverage the lack of key separation. This enables cryptographic attacks such as key reuse, potentially allowing the decryption of application data or the forging of messages in sessions derived from the same weak PSK state.
Protection from this CVE
Upgrade to Clatter v2.2.0 immediately. The patch introduces mandatory runtime checks that abort any handshake violating the PSK validity rule. As a workaround, manually audit and eliminate all use of the affected `_psk0` post-quantum handshake patterns within application code until the upgrade is performed.
Impact:
Weakened security guarantees allowing potential key reuse attacks, which could lead to loss of message confidentiality and integrity in affected communication channels.
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Sources:
Reported By: github.com
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