CVE-2026-34877

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-02 · updated 2026-07-24
Weakness: CWE-250

Description

An issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.

Affected products

mbedtls: from 2.19.0 before 3.6.6 — fixed in 3.6.6
TrustedFirmware Mbed TLS: 4.0.0

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-serialized-data/

Get alerted when CVE-2026-34877 or the next vulnerability affects your stack