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CVE-2026-39831

Estado: AnalizadaCrítica (9.1)—

The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a "no-touch-required" extension in Permissions.Extensions from PublicKeyCallback.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad en verificación de clave FIDO/U2F en golang crypto (acceso remoto sin autenticación, AV:N, PR:N, UI:N). Permite usar claves de seguridad sin contacto físico, eludiendo autenticación multifactor.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Privileged Account ManagementApplication Developer GuidanceActive Directory ConfigurationVulnerability ScanningUser TrainingUser Account Management

Tecnologías afectadas (1)

Golang — Crypto

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-39831",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-39831",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-05-22T18:51:41.233749Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.1,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.2,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "security@golang.org",
      "affectedData": [
        {
          "vendor": "golang.org/x/crypto",
          "product": "golang.org/x/crypto/ssh",
          "versions": [
            {
              "status": "affected",
              "version": "0",
              "lessThan": "0.52.0",
              "versionType": "semver"
            }
          ],
          "packageName": "golang.org/x/crypto/ssh",
          "collectionURL": "https://pkg.go.dev",
          "defaultStatus": "unaffected",
          "programRoutines": [
            {
              "name": "CertChecker.CheckCert"
            },
            {
              "name": "skECDSAPublicKey.Verify"
            },
            {
              "name": "skEd25519PublicKey.Verify"
            },
            {
              "name": "connection.serverAuthenticate"
            },
            {
              "name": "CertChecker.Authenticate"
            },
            {
              "name": "CertChecker.CheckHostKey"
            },
            {
              "name": "Certificate.Verify"
            },
            {
              "name": "Dial"
            },
            {
              "name": "NewClientConn"
            },
            {
              "name": "NewServerConn"
            }
          ]
        }
      ]
    }
  ],
  "published": "2026-05-22T04:16:22.553",
  "references": [
    {
      "url": "https://go.dev/cl/781662",
      "tags": [
        "Issue Tracking"
      ],
      "source": "security@golang.org"
    },
    {
      "url": "https://go.dev/issue/79566",
      "tags": [
        "Issue Tracking"
      ],
      "source": "security@golang.org"
    },
    {
      "url": "https://groups.google.com/g/golang-announce/c/a082jnz-LvI",
      "tags": [
        "Mailing List"
      ],
      "source": "security@golang.org"
    },
    {
      "url": "https://pkg.go.dev/vuln/GO-2026-5019",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "security@golang.org"
    }
  ],
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-862"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a \"no-touch-required\" extension in Permissions.Extensions from PublicKeyCallback."
    },
    {
      "lang": "es",
      "value": "El método Verify() para tipos de clave de seguridad FIDO/U2F (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com) no verificaba el indicador de Presencia de Usuario. Se aceptaban firmas generadas sin contacto físico, lo que permitía el uso desatendido de una clave de seguridad de hardware. Para restaurar el comportamiento anterior, devuelva una extensión 'no-touch-required' en Permissions.Extensions desde PublicKeyCallback."
    }
  ],
  "lastModified": "2026-07-23T16:10:00.137",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:golang:crypto:*:*:*:*:*:go:*:*",
              "vulnerable": true,
              "matchCriteriaId": "D540395B-31B8-4B07-8F79-F5C631BBD5C8",
              "versionEndExcluding": "0.52.0"
            }
          ],
          "operator": "OR"
        }
      ]
    }
  ],
  "sourceIdentifier": "security@golang.org"
}