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{"configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:arm:mbed_tls:*:*:*:*:*:*:*:*", "matchCriteriaId": "11EB1D49-E6D0-407C-9798-C7E631B1A03D", "versionEndExcluding": "3.6.6", "versionStartIncluding": "3.1.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "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."}], "id": "CVE-2026-34876", "lastModified": "2026-04-07T12:14:22.150", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 3.6, "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary"}]}, "published": "2026-04-02T16:16:26.180", "references": [{"source": "cve@mitre.org", "tags": ["Vendor Advisory"], "url": "https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ccm-finish-boundary-check/"}, {"source": "cve@mitre.org", "tags": ["Vendor Advisory"], "url": "https://mbed-tls.readthedocs.io/en/latest/tech-updates/security-advisories/"}], "sourceIdentifier": "cve@mitre.org", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-125"}], "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary"}]}

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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": "2026-04-07T20:02:51.688387+00:00", "value": {"mitigation_remediation": ["Update Mbed TLS to version 3.6.6 or newer.", "If an upgrade is not immediately possible, ensure that any call to mbedtls_ccm_finish validates tag_len to be no larger than the authentication buffer size.", "Review existing code for usage of the multipart CCM API and add validation checks or constraints as a temporary safeguard.", "Monitor for applications still running affected library versions and plan an upgrade."], "summary": {"action": "Apply Patch", "impact": "Information Disclosure"}, "threat_synthesis": {"affected_systems": "The vulnerability affects the Arm mbed TLS library. Public versions in the 3.x series prior to 3.6.6 are susceptible. Versions of Mbed TLS 4.x before the fix also contain the same internal validation error, but the API is not publicly exposed. Applications that use the multipart CCM API in these versions are at risk.", "description_and_impact": "The flaw is an out\u2011of\u2011bounds read in mbedtls_ccm_finish() that occurs when the multipart CCM API is called with a tag_len value larger than the 16\u2011byte authentication buffer. The read exposes adjacent memory belonging to the CCM context, allowing an attacker to retrieve sensitive data such as cryptographic keys or authentication tags. This vulnerability is classified as CWE\u2011125 and results in potential information disclosure.", "risk_and_exploitability": "The CVSS score of 7.5 indicates a high severity, while an EPSS of less than 1% points to a low likelihood of exploitation in the wild. The vulnerability is not listed in the CISA KEV catalog. Exploitation requires that an attacker can invoke the multipart CCM API with an oversized tag_len, which is typically possible only through application\u2011level code that accepts user\u2011supplied parameters. The attack vector is inferred to be application\u2011level and could occur remotely if the application processes external input. The patch in 3.6.6 eliminates the unvalidated length check, mitigating the read."}}}}, "created": "2026-04-02T20:15:52.104903+00:00", "updated": "2026-04-08T19:56:38.451030+00:00", "vendors": ["mbed-tls", "mbed-tls$PRODUCT$mbedtls"]}