What’s Vulnerable › Vulnerabilities

CVE-2026-34876

• Severity: high (CVSS 7.5 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-125

Description

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Affected products

• TrustedFirmware Mbed TLS: from 3.1.0 before 3.6.6 — fixed in 3.6.6

How to fix

Upgrade to a fixed version: TrustedFirmware Mbed TLS 3.6.6. Check the vendor advisory for mitigations.

References

• https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ccm-finish-boundary-check/
• https://mbed-tls.readthedocs.io/en/latest/tech-updates/security-advisories/

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