Vulnerability in Arm Mbed TLS
CVE-2026-34872
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).
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.003 (18.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 19th percentile — 18.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
- Arm Mbed TLS
- Arm Tf-Psa-Crypto — versions 1.0.0
Weakness classification (CWE)
References
- mbed-tls.readthedocs.io/en/latest/security-advisories/ (Vendor Advisory)
- mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory… (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-34872?
- CVE-2026-34872 is a critical-severity vulnerability in Arm Mbed TLS, classified under Improper Verification of Cryptographic Signature. CVSS score: 9.1/10. Published 2026-04-01.
- How severe is CVE-2026-34872?
- Critical severity. CVSS v3 base score is 9.1 out of 10.