CVE-2026-39984

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{"affected": [{"affectedData": [{"product": "timestamp-authority", "vendor": "sigstore", "versions": [{"status": "affected", "version": "< 2.0.6"}]}], "source": "security-advisories@github.com"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:linuxfoundation:sigstore_timestamp_authority:*:*:*:*:*:*:*:*", "matchCriteriaId": "72AC995B-D581-447D-9300-056012700B64", "versionEndExcluding": "2.0.6", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6."}, {"lang": "es", "value": "Sigstore Timestamp Authority es un servicio para emitir marcas de tiempo RFC 3161. Las versiones 2.0.5 e inferiores contienen una vulnerabilidad de omisi\u00f3n de autorizaci\u00f3n en la funci\u00f3n VerifyTimestampResponse. VerifyTimestampResponse verifica correctamente la firma de la cadena de certificados, pero las comprobaciones de restricciones espec\u00edficas de TSA en VerifyLeafCert utilizan el primer certificado no-CA de la bolsa de certificados PKCS#7 en lugar del certificado hoja de la cadena verificada. Un atacante puede explotar esto anteponiendo un certificado falsificado a la bolsa de certificados mientras el mensaje est\u00e1 firmado con una clave autorizada, haciendo que la biblioteca valide la firma contra un certificado pero realice comprobaciones de autorizaci\u00f3n contra otro. Esta vulnerabilidad solo afecta a los usuarios del paquete timestamp-authority/v2/pkg/verification y no afecta al propio servicio timestamp-authority o a sigstore-go. El problema ha sido solucionado en la versi\u00f3n 2.0.6."}], "id": "CVE-2026-39984", "lastModified": "2026-10-26T21:10:00.170", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "NONE", "baseScore": 5.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "REQUIRED", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 3.6, "source": "security-advisories@github.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-39984", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-04-16T14:00:42.548200Z", "version": "2.0.3"}}]}, "published": "2026-04-15T04:17:40.203", "references": [{"source": "security-advisories@github.com", "tags": ["Product", "Release Notes"], "url": "https://github.com/sigstore/timestamp-authority/releases/tag/v2.0.6"}, {"source": "security-advisories@github.com", "tags": ["Mitigation", "Vendor Advisory"], "url": "https://github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgh2-rrg3"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-295"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{"bugzilla": {"description": "timestamp-authority/v2/pkg/verification: improper certificate validation in verifier", "id": "2458542", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2458542"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.5", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N", "status": "draft"}, "cwe": "CWE-295", "details": ["Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6.", "A flaw was found in timestamp-authority, specifically in the timestamp-authority/v2/pkg/verification package. An attacker can exploit this issue by prepending a forged certificate to the certificate bag while the message is signed with an authorized key. This causes the library to validate the signature against one certificate but perform authorization checks against another, leading to an authorization bypass."], "mitigation": {"lang": "en:us", "value": "To mitigate this vulnerability, users of VerifyTimestampResponse can use the TSACertificate option to explicitly specify the exact certificate they expect to be used."}, "name": "CVE-2026-39984", "package_state": [{"cpe": "cpe:/a:redhat:advanced_cluster_security:4", "fix_state": "Fix deferred", "package_name": "advanced-cluster-security/rhacs-main-rhel8", "product_name": "Red Hat Advanced Cluster Security 4"}, {"cpe": "cpe:/a:redhat:advanced_cluster_security:4", "fix_state": "Fix deferred", "package_name": "advanced-cluster-security/rhacs-rhel8-operator", "product_name": "Red Hat Advanced Cluster Security 4"}, {"cpe": "cpe:/a:redhat:advanced_cluster_security:4", "fix_state": "Fix deferred", "package_name": "advanced-cluster-security/rhacs-roxctl-rhel8", "product_name": "Red Hat Advanced Cluster Security 4"}, {"cpe": "cpe:/a:redhat:advanced_cluster_security:4", "fix_state": "Fix deferred", "package_name": "advanced-cluster-security/rhacs-scanner-v4-rhel8", "product_name": "Red Hat Advanced Cluster Security 4"}, {"cpe": "cpe:/a:redhat:trusted_artifact_signer:1", "fix_state": "Fix deferred", "package_name": "rhtas/cosign-rhel9", "product_name": "Red Hat Trusted Artifact Signer"}, {"cpe": "cpe:/a:redhat:trusted_artifact_signer:1", "fix_state": "Fix deferred", "package_name": "rhtas/ec-rhel9", "product_name": "Red Hat Trusted Artifact Signer"}, {"cpe": "cpe:/a:redhat:trusted_artifact_signer:1", "fix_state": "Fix deferred", "package_name": "rhtas/gitsign-rhel9", "product_name": "Red Hat Trusted Artifact Signer"}, {"cpe": "cpe:/a:redhat:openshift_security_profiles_operator:1", "fix_state": "Fix deferred", "package_name": "compliance/openshift-security-profiles-operator-bundle", "product_name": "Security Profiles Operator"}, {"cpe": "cpe:/a:redhat:openshift_security_profiles_operator:1", "fix_state": "Fix deferred", "package_name": "compliance/openshift-security-profiles-rhel8-operator", "product_name": "Security Profiles Operator"}], "public_date": "2026-04-14T23:41:47Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-39984\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-39984\nhttps://github.com/sigstore/timestamp-authority/releases/tag/v2.0.6\nhttps://github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgh2-rrg3"], "statement": "This vulnerability allows an attacker to bypass authorization checks by prepending a forged certificate to the certificate bag. The library validates the signature against one certificate while performing authorization checks against another.\nAdditionally, a user or an automated system must actively run the `VerifyTimestampResponse` function against the attacker-supplied payload. Due to this reason, this flaw has been rated with a moderate severity.\nThis issue only impacts users of the `timestamp-authority/v2/pkg/verification` package and does not affect the `timestamp-authority` service or `sigstore-go`.", "threat_severity": "Moderate"}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,2.0.6)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "timestamp-authority", "source": "cna", "vendor": "sigstore"}, "product": "timestamp_authority", "vendor": "sigstore"}], "analysis": {"en": {"generated_at": "2026-04-15T01:50:48.318553+00:00", "value": {"mitigation_remediation": ["Upgrade to timestamp\u2011authority version\u00a02.0.6 or later", "Ensure that the VerifyTimestampResponse function is only called with certificates that originate from a trusted, validated source", "If an upgrade is not immediately possible, disable or restrict the use of the VerifyTimestampResponse function in client applications and monitor for unexpected certificate chains"], "summary": {"action": "Update Patch", "impact": "Authorization bypass via forged certificates"}, "threat_synthesis": {"affected_systems": "The affected product is the sigstore timestamp\u2011authority service. Versions 2.0.5 and earlier of the timestamp\u2011authority/v2/pkg/verification package are vulnerable. The issue was fixed in release 2.0.6.", "description_and_impact": "Sigstore Timestamp Authority implements RFC\u00a03161 timestamp verification, but the VerifyTimestampResponse function only verifies the signature chain and then incorrectly applies TSA\u2011specific constraints to the first non\u2011CA certificate in the PKCS#7 bag instead of the leaf certificate of the verified chain. An attacker can prepend a forged certificate to the bag while the signed message remains valid, causing the library to validate the signature against one certificate and apply authorization checks against another. This flaw allows an attacker to bypass authorization checks and potentially obtain timestamp responses that appear legitimately signed by an authorized key.", "risk_and_exploitability": "The CVSS score is 5.5, indicating a moderate severity. EPSS data is unavailable and the vulnerability is not listed in the CISA KEV catalog. Exploitation requires an attacker to supply a crafted PKCS#7 certificate bag to a client that uses VerifyTimestampResponse; the service itself is not vulnerable. Attackers could thus forge timestamp responses that pass verification but bypass the intended authorization checks."}}}}, "created": "2026-04-15T13:48:23.610801+00:00", "updated": "2026-04-15T13:49:14.875478+00:00", "vendors": ["sigstore", "sigstore$PRODUCT$timestamp_authority"]}