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Vulnerability record · CVE-2026-34876 · published 2 April 2026

CVE-2026-34876: Trustedfirmware mbed tls out-of-bounds read vulnerability

Trustedfirmware · Mbed Tls

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.

7.5 CVSS 3.1 High EPSS 0.50% · top 59.7% CWE-125 · Out-of-bounds read
7.5CVSS 3.1 base score
0.50%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
24 Jul 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ccm-finish-boundary-chec Vendor Advisory
https://mbed-tls.readthedocs.io/en/latest/tech-updates/security-advisories/ Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2026-34877Arm mbed tls execution with unnecessary privileges vulnerabilityAn issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session st…EPSS 0.73%9.8CVE-2026-34875Trustedfirmware mbed tls classic buffer overflow vulnerabilityAn issue was discovered in Mbed TLS through 3.6.5 and TF-PSA-Crypto 1.0.0. A buffer overflow can occur in public key export for FFDH keys.EPSS 0.60%9.8CVE-2024-49195Trustedfirmware mbed tls out-of-bounds write vulnerabilityMbed TLS 3.5.x through 3.6.x before 3.6.2 has a buffer underrun in pkwrite when writing an opaque key pairEPSS 0.63%9.8CVE-2024-45158Trustedfirmware mbed tls stack-based buffer overflow vulnerabilityAn issue was discovered in Mbed TLS 3.6 before 3.6.1. A stack buffer overflow in mbedtls_ecdsa_der_to_raw() and mbedtls_ecdsa_raw_to_der() can occur …EPSS 0.68%9.8CVE-2024-45159Trustedfirmware mbed tls improper certificate validation vulnerabilityAn issue was discovered in Mbed TLS 3.x before 3.6.1. With TLS 1.3, when a server enables optional authentication of the client, if the client-provid…EPSS 0.39%9.8CVE-2023-45199Trustedfirmware mbed tls classic buffer overflow vulnerabilityMbed TLS 3.2.x through 3.4.x before 3.5 has a Buffer Overflow that can lead to remote Code execution.EPSS 1.1%9.8CVE-2022-46393Arm mbed tls out-of-bounds read vulnerabilityAn issue was discovered in Mbed TLS before 2.28.2 and 3.x before 3.3.0. There is a potential heap-based buffer overflow and heap-based buffer over-re…EPSS 1.2%9.8CVE-2021-44732Arm mbed tls double free vulnerabilityMbed TLS before 3.0.1 has a double free in certain out-of-memory conditions, as demonstrated by an mbedtls_ssl_set_session() failure.EPSS 2.6%

Source: NIST National Vulnerability Database (record CVE-2026-34876), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.