CVE-2026-34876 Details
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.
A vulnerability allowing out-of-bounds read has been identified in Mbed TLS versions 3.1.0 prior to 3.6.6. The issue arises in the 'mbedtls_ccm_finish()' function within the CCM implementation, where the 'tag_len' parameter is not properly validated. This oversight allows attackers to read beyond the allocated 16-byte buffer into adjacent memory, potentially disclosing sensitive information such as nonce data and block cipher state. The vulnerability is exploitable through the public multipart CCM API by supplying an oversized 'tag_len' parameter.
Users are advised to upgrade to Mbed TLS 3.6.6 or later versions in the 3.6 series. For those using Mbed TLS 4.x, the vulnerability is not present in the public API, but the same validation issue exists internally. If the multipart CCM API must be used, ensure that the 'tag_len' parameter does not exceed 16 bytes and matches the length negotiated in 'mbedtls_ccm_set_lengths()'.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Apr 2, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-125 | Out-of-bounds Read | CISA-ADP |
Affected Products
| Product | Versions |
|---|---|
| trustedfirmware mbed tls | >= 3.1.0, < 3.6.6 |
CPE
Remediation
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Change History
7 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 24, 2026 | CVE Translated | [email protected] |
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Jun 5, 2026 | CPE Deprecation Remap | [email protected] |
| Apr 7, 2026 | Initial Analysis | [email protected] |
| Apr 2, 2026 | CVE Modified | CISA-ADP |
| Apr 2, 2026 | New CVE Received | [email protected] |