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.

Database specific

{
    "cna_assigner": "mitre",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34876.json",
    "unresolved_ranges": [
        {
            "extracted_events": [
                {
                    "introduced": "3.x"
                },
                {
                    "fixed": "3.6.6"
                }
            ],
            "source": "DESCRIPTION"
        }
    ]
}

References

Affected packages

Git / github.com/mbed-tls/mbedtls

Affected ranges

Type

GIT

Repo

https://github.com/mbed-tls/mbedtls

Events

Introduced

d65aeb37349ad1a50e0f6c9b694d4b5290d60e49

Fixed

0bebf8b8c7f07abe3571ded48a11aa907a1ffb20

Database specific

Show details

{
    "cpe": "cpe:2.3:a:trustedfirmware:mbed_tls:*:*:*:*:*:*:*:*",
    "extracted_events": [
        {
            "introduced": "3.1.0"
        },
        {
            "fixed": "3.6.6"
        }
    ],
    "source": "CPE_RANGE"
}

Database specific

source

"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-34876.json"