EUVD-2026-18021
GHSA-347r-37hj-5jc9
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Lifecycle Timeline
3Description
An issue was discovered in Mbed TLS 3.5.x and 3.6.x through 3.6.5 and TF-PSA-Crypto 1.0. There is a lack of contributory behavior in FFDH due to improper input validation. Using finite-field Diffie-Hellman, the other party can force the shared secret into a small set of values (lack of contributory behavior). This is a problem for protocols that depend on contributory behavior (which is not the case for TLS). The attack can be carried by the peer, or depending on the protocol by an active network attacker (person in the middle).
Analysis
Finite-field Diffie-Hellman (FFDH) in Mbed TLS 3.5.x, 3.6.0 through 3.6.5, and TF-PSA-Crypto 1.0 lacks contributory behavior due to improper validation of peer-supplied parameters, allowing an attacker to restrict the shared secret to a small set of predictable values. While the vulnerability does not directly impact TLS (which does not depend on contributory behavior), it poses a significant risk to protocols that do rely on this property, including those where an active network attacker or malicious peer can exploit the weakness. …
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