Title: Mbed TLS, Description: Se descubrió un problema en Mbed TLS 3.x anterior a 3.6.6. Una vulnerabilidad de lectura fuera de límites en mbedtls_ccm_finish() en biblioteca/ccm.c permite a los atacantes obtener datos de contexto CCM adyacentes mediante la invocación de la API CCM multiparte con un parámetro tag_len de tamaño excesivo. Esto es causado por la falta de validación del parámetro tag_len contra el tamaño del búfer de autenticación interno de 16 bytes. El problema afecta a la API CCM multiparte pública en Mbed TLS 3.x, donde mbedtls_ccm_finish() puede ser invocado directamente por las aplicaciones. En las versiones de Mbed TLS 4.x anteriores a la corrección, la misma falta de validación existe en la implementación interna; sin embargo, la función no está expuesta como parte de la API pública. La explotación requiere la invocación a nivel de aplicación de la API CCM multiparte.

{"timestamp":"2026-04-02T15:53:54.288854Z","id":"CVE-2026-34876","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}

[{"vendor":"n/a","product":"n/a","versions":[{"version":"n/a","status":"affected"}]}]

OR
     *cpe:2.3:a:arm:mbed_tls:*:*:*:*:*:*:*:* versions from (including) 3.1.0 from (excluding) 3.6.6

OR
     *cpe:2.3:a:trustedfirmware:mbed_tls:*:*:*:*:*:*:*:* versions from (including) 3.1.0 from (excluding) 3.6.6

OR
          *cpe:2.3:a:arm:mbed_tls:*:*:*:*:*:*:*:* versions from (including) 3.1.0 up to (excluding) 3.6.6

MITRE: https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ccm-finish-boundary-check/ Types: Vendor Advisory

MITRE: https://mbed-tls.readthedocs.io/en/latest/tech-updates/security-advisories/ Types: Vendor Advisory

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CWE-125

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.

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/