CVE-2026-34872 Weak cryptography in n/a

Critical 9.1 Published 1 Apr 2026 Updated 1 Apr 2026

Attackers can force shared secrets into small sets in FFDH due to improper input validation, compromising protocols relying on contributory behavior.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-34872?

CVE-2026-34872 is a critical vulnerability in Arm Mbed Tls, published on 1 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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).

Weakness: CWE-347

Which versions are affected by CVE-2026-34872?

It affects 2 products.

Products include Arm Mbed Tls, Arm Tf-Psa-Crypto.

How do I fix CVE-2026-34872?

Upgrade to a fixed version.

Is CVE-2026-34872 being exploited?

There is no known exploitation of CVE-2026-34872 in the wild and no public exploit code.

All Arm Mbed Tls vulnerabilities

Sources

Also known as DEBIAN-CVE-2026-34872, ECHO-8e44-1e55-58a6, GHSA-347r-37hj-5jc9, JLSEC-2026-466, ROOT-OS-DEBIAN-12-CVE-2026-34872, UBUNTU-CVE-2026-34872.