Vulnerability 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 Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Arm | Mbed Tls | >= 3.1.0, < 3.6.6 |
Related Weaknesses (CWE)
References
- https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-aVendor Advisory
- https://mbed-tls.readthedocs.io/en/latest/tech-updates/security-advisories/Vendor Advisory
FAQ
What is CVE-2026-34876?
CVE-2026-34876 is a vulnerability with a CVSS score of 7.5 (HIGH). 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 o...
How severe is CVE-2026-34876?
CVE-2026-34876 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-34876?
Check the references section above for vendor advisories and patch information. Affected products include: Arm Mbed Tls.