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🚨 Security Advisory: 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.
A new vulnerability has been identified and published under CVE-2026-34876 as part of Microsoft’s Security Update Guide on Tue, 02 Jun 2026 01:46:41 -0700.
Organizations should review this advisory to understand potential risks, affected systems, and recommended mitigation steps. Timely awareness of vulnerabilities is critical for maintaining a strong cybersecurity posture and reducing exposure to emerging threats.
🔎 What this means for you:
This vulnerability may impact systems, applications, or services commonly used in enterprise environments. Security teams should evaluate exposure and apply updates or mitigations as soon as possible.
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.
🛡️ Recommended Actions
- Review the full advisory from Microsoft: View advisory
- Identify affected systems within your environment
- Apply patches or mitigations where applicable
- Monitor for suspicious activity related to this vulnerability
📡 Stay Ahead of Threats
This post is part of DataComm's vulnerability intelligence feed designed to keep your organization informed of the latest security risks.
For deeper insights, threat detection, and response capabilities, consider implementing a banking-grade security strategy that includes continuous monitoring, threat intelligence, and rapid incident response.
Our Status
DataComm is reviewing affected systems and validating compliance in accordance with vendor guidance. Customers requiring assistance are encouraged to contact our support team.
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Source: Microsoft Security Response Center (MSRC)
