FKIE_CVE-2020-26891

Vulnerability from fkie_nvd - Published: 2020-10-19 17:15 - Updated: 2026-06-17 03:08
Severity
6.1 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Summary
AuthRestServlet in Matrix Synapse before 1.21.0 is vulnerable to XSS due to unsafe interpolation of the session GET parameter. This allows a remote attacker to execute an XSS attack on the domain Synapse is hosted on, by supplying the victim user with a malicious URL to the /_matrix/client/r0/auth/*/fallback/web or /_matrix/client/unstable/auth/*/fallback/web Synapse endpoints.
References
cve@mitre.orghttps://github.com/matrix-org/synapse/pull/8444Issue Tracking, Patch, Third Party Advisory
cve@mitre.orghttps://github.com/matrix-org/synapse/releases/tag/v1.21.2Release Notes, Third Party Advisory
cve@mitre.orghttps://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmqPatch, Third Party Advisory
cve@mitre.orghttps://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisoryRelease Notes, Vendor Advisory
af854a3a-2127-422b-91ae-364da2661108https://github.com/matrix-org/synapse/pull/8444Issue Tracking, Patch, Third Party Advisory
af854a3a-2127-422b-91ae-364da2661108https://github.com/matrix-org/synapse/releases/tag/v1.21.2Release Notes, Third Party Advisory
af854a3a-2127-422b-91ae-364da2661108https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmqPatch, Third Party Advisory
af854a3a-2127-422b-91ae-364da2661108https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisoryRelease Notes, Vendor Advisory
Impacted products
Vendor Product Version
matrix synapse *
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "n/a",
          "vendor": "n/a",
          "versions": [
            {
              "status": "affected",
              "version": "n/a"
            }
          ]
        }
      ],
      "source": "cve@mitre.org"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "39E3BC16-D440-463F-BC7B-B640865B60B4",
              "versionEndExcluding": "1.21.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "AuthRestServlet in Matrix Synapse before 1.21.0 is vulnerable to XSS due to unsafe interpolation of the session GET parameter. This allows a remote attacker to execute an XSS attack on the domain Synapse is hosted on, by supplying the victim user with a malicious URL to the /_matrix/client/r0/auth/*/fallback/web or /_matrix/client/unstable/auth/*/fallback/web Synapse endpoints."
    },
    {
      "lang": "es",
      "value": "AuthRestServlet en Matrix Synapse versiones anteriores a 1.21.0 es vulnerable a XSS debido a la interpolaci\u00f3n insegura del par\u00e1metro GET de la sesi\u00f3n. Esto permite a un atacante remoto ejecutar un ataque XSS en el dominio en el que est\u00e1 alojado Synapse, suministrando al usuario v\u00edctima una URL maliciosa a los puntos finales de /_matrix/cliente/r0/auth/*/fallback/web o /_matrix/cliente/instable/auth/*/fallback/web Synapse"
    }
  ],
  "id": "CVE-2020-26891",
  "lastModified": "2026-06-17T03:08:28.523",
  "metrics": {
    "cvssMetricV2": [
      {
        "acInsufInfo": false,
        "baseSeverity": "MEDIUM",
        "cvssData": {
          "accessComplexity": "MEDIUM",
          "accessVector": "NETWORK",
          "authentication": "NONE",
          "availabilityImpact": "NONE",
          "baseScore": 4.3,
          "confidentialityImpact": "NONE",
          "integrityImpact": "PARTIAL",
          "vectorString": "AV:N/AC:M/Au:N/C:N/I:P/A:N",
          "version": "2.0"
        },
        "exploitabilityScore": 8.6,
        "impactScore": 2.9,
        "obtainAllPrivilege": false,
        "obtainOtherPrivilege": false,
        "obtainUserPrivilege": false,
        "source": "nvd@nist.gov",
        "type": "Primary",
        "userInteractionRequired": true
      }
    ],
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 6.1,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 2.7,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  },
  "published": "2020-10-19T17:15:13.220",
  "references": [
    {
      "source": "cve@mitre.org",
      "tags": [
        "Issue Tracking",
        "Patch",
        "Third Party Advisory"
      ],
      "url": "https://github.com/matrix-org/synapse/pull/8444"
    },
    {
      "source": "cve@mitre.org",
      "tags": [
        "Release Notes",
        "Third Party Advisory"
      ],
      "url": "https://github.com/matrix-org/synapse/releases/tag/v1.21.2"
    },
    {
      "source": "cve@mitre.org",
      "tags": [
        "Patch",
        "Third Party Advisory"
      ],
      "url": "https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq"
    },
    {
      "source": "cve@mitre.org",
      "tags": [
        "Release Notes",
        "Vendor Advisory"
      ],
      "url": "https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Issue Tracking",
        "Patch",
        "Third Party Advisory"
      ],
      "url": "https://github.com/matrix-org/synapse/pull/8444"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Release Notes",
        "Third Party Advisory"
      ],
      "url": "https://github.com/matrix-org/synapse/releases/tag/v1.21.2"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Patch",
        "Third Party Advisory"
      ],
      "url": "https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Release Notes",
        "Vendor Advisory"
      ],
      "url": "https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory"
    }
  ],
  "sourceIdentifier": "cve@mitre.org",
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
        }
      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    }
  ]
}



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