mbed TLS up to 3.6.5 Multipart CCM API library/ccm.c mbedtls_ccm_finish tag_len out-of-bounds

Summaryinfo

A vulnerability was found in mbed TLS up to 3.6.5. It has been declared as problematic. This affects the function mbedtls_ccm_finish of the file library/ccm.c of the component Multipart CCM API. Executing a manipulation of the argument tag_len can lead to out-of-bounds. The identification of this vulnerability is CVE-2026-34876. The attack may be launched remotely. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in mbed TLS up to 3.6.5. This vulnerability affects the function mbedtls_ccm_finish of the file library/ccm.c of the component Multipart CCM API. The manipulation of the argument tag_len with an unknown input leads to a out-of-bounds vulnerability. The CWE definition for the vulnerability is CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. As an impact it is known to affect confidentiality. CVE summarizes:

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.

The advisory is available at mbed-tls.readthedocs.io. This vulnerability was named CVE-2026-34876 since 03/31/2026. The exploitation appears to be easy. The attack can be initiated remotely. Technical details are known, but there is no available exploit.

Upgrading to version 3.6.6 eliminates this vulnerability.

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Productinfo

Name

• mbed TLS

Version

• 3.6.0
• 3.6.1
• 3.6.2
• 3.6.3
• 3.6.4
• 3.6.5

CPE 2.3info

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CPE 2.2info

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