CVE-2026-39984

{
  "id": "CVE-2026-39984",
  "sourceIdentifier": "[email protected]",
  "published": "2026-04-15T04:17:40.203",
  "lastModified": "2026-10-26T21:10:00.170",
  "vulnStatus": "Analyzed",
  "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 omisión de autorización en la función VerifyTimestampResponse. VerifyTimestampResponse verifica correctamente la firma de la cadena de certificados, pero las comprobaciones de restricciones específicas 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 está firmado con una clave autorizada, haciendo que la biblioteca valide la firma contra un certificado pero realice comprobaciones de autorización 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 versión 2.0.6."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "sigstore",
          "product": "timestamp-authority",
          "versions": [
            {
              "version": "< 2.0.6",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N",
          "baseScore": 5.5,
          "baseSeverity": "MEDIUM",
          "attackVector": "LOCAL",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "REQUIRED",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "availabilityImpact": "NONE"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 3.6
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-04-16T14:00:42.548200Z",
          "id": "CVE-2026-39984",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-295"
        }
      ]
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "operator": "OR",
          "negate": false,
          "cpeMatch": [
            {
              "vulnerable": true,
              "criteria": "cpe:2.3:a:linuxfoundation:sigstore_timestamp_authority:*:*:*:*:*:*:*:*",
              "versionEndExcluding": "2.0.6",
              "matchCriteriaId": "72AC995B-D581-447D-9300-056012700B64"
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  "references": [
    {
      "url": "https://github.com/sigstore/timestamp-authority/releases/tag/v2.0.6",
      "source": "[email protected]",
      "tags": [
        "Product",
        "Release Notes"
      ]
    },
    {
      "url": "https://github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgh2-rrg3",
      "source": "[email protected]",
      "tags": [
        "Mitigation",
        "Vendor Advisory"
      ]
    }
  ]
}