{"dataType": "CVE_RECORD", "cveMetadata": {"state": "PUBLISHED", "cveId": "CVE-2026-34876", "assignerOrgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca", "assignerShortName": "mitre", "dateUpdated": "2026-04-02T15:54:45.230Z", "dateReserved": "2026-03-31T00:00:00.000Z", "datePublished": "2026-04-02T00:00:00.000Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca", "shortName": "mitre", "dateUpdated": "2026-04-02T15:08:59.859Z"}, "descriptions": [{"lang": "en", "value": "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."}], "affected": [{"vendor": "n/a", "product": "n/a", "versions": [{"version": "n/a", "status": "affected"}]}], "references": [{"url": "https://mbed-tls.readthedocs.io/en/latest/tech-updates/security-advisories/"}, {"url": "https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ccm-finish-boundary-check/"}], "problemTypes": [{"descriptions": [{"type": "text", "lang": "en", "description": "n/a"}]}]}, "adp": [{"problemTypes": [{"descriptions": [{"type": "CWE", "cweId": "CWE-125", "lang": "en", "description": "CWE-125 Out-of-bounds Read"}]}], "metrics": [{"cvssV3_1": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 7.5, "attackVector": "NETWORK", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}}, {"other": {"type": "ssvc", "content": {"timestamp": "2026-04-02T15:53:54.288854Z", "id": "CVE-2026-34876", "options": [{"Exploitation": "none"}, {"Automatable": "yes"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-04-02T15:54:45.230Z"}}]}, "dataVersion": "5.2"}

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{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,3.6.6)"}}], "enrichment": {"confidence": 90.0, "confidence_source": "inferred", "scores": [{"score": 90.0, "source": "inferred"}, {"score": 97.0, "source": "matching"}]}, "original": {"product": "n/a", "source": "cna", "vendor": "n/a"}, "product": "mbedtls", "vendor": "mbed-tls"}], "analysis": {"en": {"generated_at": "2026-04-02T16:27:52.065686+00:00", "value": {"mitigation_remediation": ["Upgrade Mbed TLS to version 3.6.6 or later, which includes bounds checking in mbedtls_ccm_finish().", "If using Mbed TLS 4.x, apply the internal fix that adds tag_len validation to the implementation.", "For environments where an immediate upgrade is not possible, add application\u2011level validation to ensure tag_len does not exceed the 16\u2011byte authentication buffer or disable the multipart CCM API until a patched version is available."], "summary": {"action": "Immediate Patch", "impact": "Information Disclosure via Out\u2011of\u2011Bounds Read"}, "threat_synthesis": {"affected_systems": "The vulnerability affects the open\u2011source Mbed TLS cryptographic library. All 3.x releases prior to 3.6.6 are exposed, as the public multipart CCM API allows direct invocation of mbedtls_ccm_finish(). Mbed TLS 4.x contains the same internal missing validation, but the function is not publicly exposed, so the risk is limited to library developers. No vendor or product name beyond Mbed TLS is listed.", "description_and_impact": "Mbed TLS 3.x before version 3.6.6 contains an out\u2011of\u2011bounds read in the function mbedtls_ccm_finish() where the tag_len parameter is not validated against the internal 16\u2011byte authentication buffer. An attacker who can invoke the multipart CCM API may supply an oversized tag_len and read data that lies just beyond the intended buffer. This allows the leakage of adjacent CCM context data, potentially exposing sensitive authentication material and compromising confidentiality.", "risk_and_exploitability": "Exploitation requires application\u2011level use of the multipart CCM API and the ability to supply an oversized tag_len. It does not provide remote code execution or denial of service, but it enables covert data leakage. The EPSS score is not available and the vulnerability is not listed in CISA\u2019s KEV catalog, indicating no confirmed widespread exploitation yet. However, the CVSS score is high enough that any system using the affected library should apply the patch promptly."}}}}, "created": "2026-04-02T20:15:52.104903+00:00", "title": "Out\u2011of\u2011Bounds Read in Mbed TLS CCM API Enabling Information Disclosure", "updated": "2026-04-02T20:22:23.974738+00:00", "vendors": ["mbed-tls", "mbed-tls$PRODUCT$mbedtls"], "weaknesses": ["CWE-119", "CWE-200"]}