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CVE-2021-21239

Estado: ModificadaMedia (6.5)—

PySAML2 is a pure python implementation of SAML Version 2 Standard. PySAML2 before 6.5.0 has an improper verification of cryptographic signature vulnerability. Users of pysaml2 that use the default CryptoBackendXmlSec1 backend and need to verify signed SAML documents are impacted. PySAML2 does not ensure that a signed SAML document is correctly signed. The default CryptoBackendXmlSec1 backend is using the xmlsec1 binary to verify the signature of signed SAML documents, but by default xmlsec1 accepts any type of key found within the given document. xmlsec1 needs to be configured explicitly to only use only _x509 certificates_ for the verification process of the SAML document signature. This is fixed in PySAML2 6.5.0.

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).

Tecnologías afectadas (2)

Debian — Debian LinuxPysaml2 Project — Pysaml2

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2021-21239",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 4.3,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:M/Au:N/C:N/I:P/A:N",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "MEDIUM",
          "availabilityImpact": "NONE",
          "confidentialityImpact": "NONE"
        },
        "acInsufInfo": false,
        "impactScore": 2.9,
        "baseSeverity": "MEDIUM",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 8.6,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": true
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
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        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.5,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N",
          "integrityImpact": "HIGH",
          "userInteraction": "REQUIRED",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 2.8
      },
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
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          "attackVector": "NETWORK",
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          "confidentialityImpact": "NONE"
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        "exploitabilityScore": 2.8
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  },
  "affected": [
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      "affectedData": [
        {
          "vendor": "IdentityPython",
          "product": "pysaml2",
          "versions": [
            {
              "status": "affected",
              "version": "< 6.5.0"
            }
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      ]
    }
  ],
  "published": "2021-01-21T15:15:14.423",
  "references": [
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    },
    {
      "url": "https://www.aleksey.com/pipermail/xmlsec/2013/009717.html",
      "tags": [
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        "Mailing List",
        "Third Party Advisory"
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-347"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "PySAML2 is a pure python implementation of SAML Version 2 Standard. PySAML2 before 6.5.0 has an improper verification of cryptographic signature vulnerability. Users of pysaml2 that use the default CryptoBackendXmlSec1 backend and need to verify signed SAML documents are impacted. PySAML2 does not ensure that a signed SAML document is correctly signed. The default CryptoBackendXmlSec1 backend is using the xmlsec1 binary to verify the signature of signed SAML documents, but by default xmlsec1 accepts any type of key found within the given document. xmlsec1 needs to be configured explicitly to only use only _x509 certificates_ for the verification process of the SAML document signature. This is fixed in PySAML2 6.5.0."
    },
    {
      "lang": "es",
      "value": "PySAML2 es una implementación de Python pura de SAML Versión 2 Estándar. PySAML2 versiones anteriores a 6.5.0, presenta una verificación inapropiada de una vulnerabilidad de firma criptográfica. Los usuarios de pysaml2 que utilizan el backend CryptoBackendXmlSec1 predeterminado y necesitan verificar los documentos SAML firmados están afectados. PySAML2 no garantiza que un documento SAML firmado esté correctamente firmado. El backend CryptoBackendXmlSec1 predeterminado está usando el binario xmlsec1 para verificar la firma de los documentos SAML firmados, pero por defecto xmlsec1 acepta cualquier tipo de clave que se encuentre dentro del documento dado. xmlsec1 debe configurarse explícitamente para usar solo _x509 certificates_ para el proceso de verificación de la firma del documento SAML. Esto es corregido en PySAML2 versión 6.5.0"
    }
  ],
  "lastModified": "2026-06-17T03:35:06.293",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:pysaml2_project:pysaml2:*:*:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "A94B9227-93A8-4D3D-A8C3-E56F3A84F8B2",
              "versionEndExcluding": "6.5.0"
            }
          ],
          "operator": "OR"
        }
      ]
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      "nodes": [
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          "negate": false,
          "cpeMatch": [
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            }
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          "operator": "OR"
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  "sourceIdentifier": "security-advisories@github.com"
}