CVE-2026-34872 - mbedtls: Mbed TLS and TF-PSA-Crypto: Shared secret manipulation via improper FFDH input validation

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CRITICAL

mbedtls: Mbed TLS and TF-PSA-Crypto: Shared secret manipulation via improper FFDH input validation

Published Apr 1, 2026

9.1

CRITICAL

CVSS 3.1

EPSS 0.28%

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

Remediation

Red Hat statement

An Important flaw exists in Mbed TLS and TF-PSA-Crypto due to improper input validation in the finite-field Diffie-Hellman (FFDH) key exchange. This allows a remote attacker to influence the shared secret to a small set of values, impacting protocols that rely on strong contributory behavior. Notably, the TLS protocol is not affected by this specific issue.

Red Hat mitigation

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Weaknesses (2)

CWE-1287

CWE-347

References (7)

https://access.redhat.com/security/cve/CVE-2026-34872
Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2453966
Issue Tracking
https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-18021
Advisory
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/
MitigationVendor Advisory
https://nvd.nist.gov/vuln/detail/CVE-2026-34872
https://www.cve.org/CVERecord?id=CVE-2026-34872

Link	Providers	Tags
https://access.redhat.com/security/cve/CVE-2026-34872		Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2453966		Issue Tracking
https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-18021		Advisory
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/		MitigationVendor Advisory
https://nvd.nist.gov/vuln/detail/CVE-2026-34872
https://www.cve.org/CVERecord?id=CVE-2026-34872