CVE-2026-34876: trustedfirmware mbed_tls Out-of-bounds Read

Vulnerability summary

CVE-2026-34876 is a high (CVSS 7.5) Out-of-bounds Read vulnerability in trustedfirmware mbed_tls. EPSS estimates a 0.50% chance of exploitation in the next 30 days, higher than 41.5% of scored vulnerabilities.

Timeline

1. 02-04-2026
   PublishedVulnerability first disclosed.
2. 02-04-2026
   Last modifiedVulnerability information updated.

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.

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.