CVE-2026-34876

mbedtls: An issue was discovered in Mbed TLS 3.x before 3.6.6

CVE-2026-34876 is fixed in mbedtls on 1 platform, first by DEBIAN-CVE-2026-34876, released April 2, 2026. It is not reported as exploited. Patch Radar priority: High.

High
CVSS
7.5
high
Exploitation
None reported
No vendor assessment
CISA KEV
Not listed
Not in the Known Exploited Vulnerabilities catalog
EPSS
0.0041
35th percentile

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.

Where it's fixed

ProductFixed inFixReleased
Linux
mbedtls · Debian 13.5 (trixie) 3.6.6-0.1~deb13u1 DEBIAN-CVE-2026-34876 Apr 2, 2026
mbedtls · Debian 14 3.6.6-0.1 DEBIAN-CVE-2026-34876 Apr 2, 2026

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