CVE-2026-34877
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk35th percentile - higher than 35% of all known CVEs
Summary
A vulnerability in Mbed TLS (versions 2.19.0 to 3.6.5 and 4.0.0) is caused by insufficient protection of serialized SSL structures. An attacker can modify these structures, leading to memory corruption and potential arbitrary code execution.
Risk Assessment
Risk of application takeover, potentially leading to full system compromise and data breach.
Recommendation
Update Mbed TLS to version 3.6.6 or later (or 4.1.0) if available. Restrict access to serialized SSL session data.
Other vulnerabilities in Mbed TLS
See all- CVE-2026-73064Low
In Mbed TLS 3.2.0 through 3.6.6 and 4.0.0 through 4.1.0, an attacker who can cause an entropy source to fail can remove or inject bytes into the start of the TLS stream. This only affects TLS 1.3 servers.
- CVE-2026-25832Low
In Mbed TLS 3.6.x before 3.6.7 and 4.1.x before 4.1.2, the TLS 1.3 client accepts a HelloRetryRequest selecting a group that was not advertised. This can violate TLS 1.3 protocol negotiation expectations.
- CVE-2026-34876High
Mbed TLS 3.x before 3.6.6 has an out-of-bounds read vulnerability in mbedtls_ccm_finish() due to missing validation of the tag_len parameter. An attacker can obtain adjacent CCM context data.
Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS