What’s Vulnerable › Vulnerabilities

CVE-2026-34872

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-01 · updated 2026-06-17
• Weakness: CWE-347

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).

Affected products

• mbedtls: before 3.6.6 — fixed in 3.6.6
• Arm Tf-Psa-Crypto: 1.0.0

How to fix

Upgrade to a fixed version: mbedtls 3.6.6. Check the vendor advisory for mitigations.

References

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

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