{"id":"UBUNTU-CVE-2026-34876","details":"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.","modified":"2026-05-20T16:25:34.747303116Z","published":"2026-04-02T16:16:00Z","upstream":["CVE-2026-34876"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-34876"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-34876"},{"type":"REPORT","url":"https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ccm-finish-boundary-check/"}],"affected":[{"package":{"name":"mbedtls","ecosystem":"Ubuntu:16.04:LTS","purl":"pkg:deb/ubuntu/mbedtls?arch=source&distro=xenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.1.2-1","2.2.0-1","2.2.1-1","2.2.1-2","2.2.1-2ubuntu0.1","2.2.1-2ubuntu0.2","2.2.1-2ubuntu0.3"],"ecosystem_specific":{"binaries":[{"binary_name":"libmbedcrypto0","binary_version":"2.2.1-2ubuntu0.3"},{"binary_name":"libmbedtls10","binary_version":"2.2.1-2ubuntu0.3"},{"binary_name":"libmbedx509-0","binary_version":"2.2.1-2ubuntu0.3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-34876.json"}},{"package":{"name":"mbedtls","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/mbedtls?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.5.1-1ubuntu1","2.6.0-1","2.7.0-2","2.8.0-1","2.8.0-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libmbedcrypto1","binary_version":"2.8.0-1ubuntu0.1~esm1"},{"binary_version":"2.8.0-1ubuntu0.1~esm1","binary_name":"libmbedtls10"},{"binary_name":"libmbedx509-0","binary_version":"2.8.0-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-34876.json"}},{"package":{"name":"mbedtls","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/mbedtls?arch=source&distro=esm-apps%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.16.2-1","2.16.3-1","2.16.4-1ubuntu2","2.16.4-1ubuntu2+esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libmbedcrypto3","binary_version":"2.16.4-1ubuntu2+esm1"},{"binary_version":"2.16.4-1ubuntu2+esm1","binary_name":"libmbedtls12"},{"binary_name":"libmbedx509-0","binary_version":"2.16.4-1ubuntu2+esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-34876.json"}},{"package":{"name":"mbedtls","ecosystem":"Ubuntu:Pro:22.04:LTS","purl":"pkg:deb/ubuntu/mbedtls?arch=source&distro=esm-apps%2Fjammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.16.9-0.1ubuntu1","2.16.11-0.1ubuntu1","2.16.11-0.3","2.28.0-1","2.28.0-1build1","2.28.0-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libmbedcrypto7","binary_version":"2.28.0-1ubuntu0.1~esm1"},{"binary_version":"2.28.0-1ubuntu0.1~esm1","binary_name":"libmbedtls14"},{"binary_name":"libmbedx509-1","binary_version":"2.28.0-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-34876.json"}},{"package":{"name":"mbedtls","ecosystem":"Ubuntu:Pro:24.04:LTS","purl":"pkg:deb/ubuntu/mbedtls?arch=source&distro=esm-apps%2Fnoble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.28.3-1","2.28.6-1ubuntu1","2.28.7-1ubuntu1","2.28.7-1.1ubuntu1","2.28.8-1","2.28.8-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"2.28.8-1ubuntu0.1~esm1","binary_name":"libmbedcrypto7t64"},{"binary_name":"libmbedtls14t64","binary_version":"2.28.8-1ubuntu0.1~esm1"},{"binary_name":"libmbedx509-1t64","binary_version":"2.28.8-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-34876.json"}},{"package":{"name":"mbedtls","ecosystem":"Ubuntu:25.10","purl":"pkg:deb/ubuntu/mbedtls?arch=source&distro=questing"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.6.2-3ubuntu1"],"ecosystem_specific":{"binaries":[{"binary_version":"3.6.2-3ubuntu1","binary_name":"libmbedcrypto16"},{"binary_version":"3.6.2-3ubuntu1","binary_name":"libmbedtls21"},{"binary_name":"libmbedx509-7","binary_version":"3.6.2-3ubuntu1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-34876.json"}},{"package":{"name":"mbedtls","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/mbedtls?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.6.2-3ubuntu1","3.6.5-0.1ubuntu1","3.6.5-0.1ubuntu2"],"ecosystem_specific":{"binaries":[{"binary_name":"libmbedcrypto16","binary_version":"3.6.5-0.1ubuntu2"},{"binary_name":"libmbedtls21","binary_version":"3.6.5-0.1ubuntu2"},{"binary_name":"libmbedx509-7","binary_version":"3.6.5-0.1ubuntu2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-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