VulnerabilityAnalyzed

CVE-2026-34872

There is a lack of contributory behavior in FFDH due to improper input validation.

CRITICAL 9.1EPSS 0.20%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.20%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

Description

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).

CVSS 3.1: 9.1 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS: 0.20% probability · 11th percentile
CISA KEV: Not listed
Weakness: CWE-347
Affected: arm/mbed tls · arm/tf-psa-crypto
Source: cve@mitre.org

References

https://mbed-tls.readthedocs.io/en/latest/security-advisories/Vendor Advisory
https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ffdh-peerkey-checks/Mitigation, Vendor Advisory

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.