Vulnerability Details CVE-2026-34876
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 7.9%
CVSS Severity
CVSS v3 Score 7.5
References
Products affected by CVE-2026-34876
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cpe:2.3:a:trustedfirmware:mbed_tls:3.1.0
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cpe:2.3:a:trustedfirmware:mbed_tls:3.2.0
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cpe:2.3:a:trustedfirmware:mbed_tls:3.2.1
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cpe:2.3:a:trustedfirmware:mbed_tls:3.3.0
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cpe:2.3:a:trustedfirmware:mbed_tls:3.4.0
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cpe:2.3:a:trustedfirmware:mbed_tls:3.4.1
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cpe:2.3:a:trustedfirmware:mbed_tls:3.5.0
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cpe:2.3:a:trustedfirmware:mbed_tls:3.5.1
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cpe:2.3:a:trustedfirmware:mbed_tls:3.5.2
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cpe:2.3:a:trustedfirmware:mbed_tls:3.6.0
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cpe:2.3:a:trustedfirmware:mbed_tls:3.6.1
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cpe:2.3:a:trustedfirmware:mbed_tls:3.6.2
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cpe:2.3:a:trustedfirmware:mbed_tls:3.6.3
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cpe:2.3:a:trustedfirmware:mbed_tls:3.6.4
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cpe:2.3:a:trustedfirmware:mbed_tls:3.6.5