CVE-2026-34876

7.5 HIGH 0.4% exploit odds Fix listed Memory safety Library

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. High risk of data exposure.
Exploit odds: 0.4% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-04-02 16:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-07-24 21:10 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.4% in the next 30 days (EPSS).
Severity: 7.5 HIGH (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-04-02 16:16 UTC
Last modified: 2026-07-24 21:10 UTC
Exploit probability: 0.4% · EPSS, next 30 days
Weakness: CWE-125 · Out-of-bounds read
Record status: Analyzed

Affected

Trustedfirmware Mbed Tls < 3.6.6

Attack profile CVSS 3.1 · 7.5

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Raw vector

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

Is it in your code?

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Fix and advisories

References

NVD record · CVE.org record