Out-of-Bounds Read Vulnerability in Mbed TLS 3.x by Arm
CVE-2026-34876

7.5HIGH

Key Information:

Vendor

Arm
Status
Mbed TLS
Vendor
CVE Published:
2 April 2026

What is CVE-2026-34876?

An out-of-bounds read vulnerability has been identified in Mbed TLS 3.x versions preceding 3.6.6. This vulnerability exists within the mbedtls_ccm_finish() function in library/ccm.c, allowing attackers to access adjacent CCM context data. This occurs when the multipart CCM API is invoked with an oversized tag_len parameter, due to inadequate validation against the internal 16-byte authentication buffer's size. While Mbed TLS 4.x contains similar validation issues in its internal implementation, it does not expose the flawed function in its public API. Successful exploitation necessitates invoking the multipart CCM API directly within applications.

References

https://mbed-tls.readthedocs.io/en/latest/tech-updates/se...
https://mbed-tls.readthedocs.io/en/latest/security-adviso...

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
High
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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