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CVE-2021-22538

Status: ModifiedHigh (8.8)—

A privilege escalation vulnerability impacting the Google Exposure Notification Verification Server (versions prior to 0.23.1), allows an attacker who (1) has UserWrite permissions and (2) is using a carefully crafted request or malicious proxy, to create another user with higher privileges than their own. This occurs due to insufficient checks on the allowed set of permissions. The new user creation event would be captured in the Event Log.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (1)

Google — Exposure Notifications Verification Server

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-22538",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 6.5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:L/Au:S/C:P/I:P/A:P",
          "authentication": "SINGLE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "LOW",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "PARTIAL"
        },
        "acInsufInfo": false,
        "impactScore": 6.4,
        "baseSeverity": "MEDIUM",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 8,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": false
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "cve-coordination@google.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.3,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "LOW",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "LOW"
        },
        "impactScore": 3.4,
        "exploitabilityScore": 2.8
      },
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 8.8,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 2.8
      }
    ]
  },
  "affected": [
    {
      "source": "cve-coordination@google.com",
      "affectedData": [
        {
          "vendor": "Google LLC",
          "product": "Exposure Notifications Verification Server",
          "versions": [
            {
              "status": "affected",
              "version": "stable",
              "versionType": "custom",
              "lessThanOrEqual": "0.23.0"
            }
          ],
          "platforms": [
            "all"
          ]
        }
      ]
    }
  ],
  "published": "2021-03-31T21:15:16.057",
  "references": [
    {
      "url": "https://github.com/google/exposure-notifications-verification-server/commit/eb8cf40b12dbe79304f1133c06fb73419383cd95",
      "tags": [
        "Patch",
        "Third Party Advisory"
      ],
      "source": "cve-coordination@google.com"
    },
    {
      "url": "https://github.com/google/exposure-notifications-verification-server/releases/tag/v0.23.1",
      "tags": [
        "Release Notes",
        "Third Party Advisory"
      ],
      "source": "cve-coordination@google.com"
    },
    {
      "url": "https://github.com/google/exposure-notifications-verification-server/releases/tag/v0.24.0",
      "tags": [
        "Release Notes",
        "Third Party Advisory"
      ],
      "source": "cve-coordination@google.com"
    },
    {
      "url": "https://github.com/google/exposure-notifications-verification-server/security/advisories/GHSA-5v95-v8c8-3rh6",
      "tags": [
        "Third Party Advisory"
      ],
      "source": "cve-coordination@google.com"
    },
    {
      "url": "https://github.com/google/exposure-notifications-verification-server/commit/eb8cf40b12dbe79304f1133c06fb73419383cd95",
      "tags": [
        "Patch",
        "Third Party Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://github.com/google/exposure-notifications-verification-server/releases/tag/v0.23.1",
      "tags": [
        "Release Notes",
        "Third Party Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://github.com/google/exposure-notifications-verification-server/releases/tag/v0.24.0",
      "tags": [
        "Release Notes",
        "Third Party Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://github.com/google/exposure-notifications-verification-server/security/advisories/GHSA-5v95-v8c8-3rh6",
      "tags": [
        "Third Party Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "cve-coordination@google.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        }
      ]
    },
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-276"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "A privilege escalation vulnerability impacting the Google Exposure Notification Verification Server (versions prior to 0.23.1), allows an attacker who (1) has UserWrite permissions and (2) is using a carefully crafted request or malicious proxy, to create another user with higher privileges than their own. This occurs due to insufficient checks on the allowed set of permissions. The new user creation event would be captured in the Event Log."
    },
    {
      "lang": "es",
      "value": "Una vulnerabilidad de escalada de privilegios que afecta al Google Exposure Notification Verification Server (versiones anteriores a 0.23.1), permite a un atacante que (1) tenga permisos de UserWrite y (2) esté usando una petición cuidadosamente diseñada o un proxy malicioso, crear otro usuario con un nivel de privilegios mayores que los suyos. Esto se presenta debido a controles insuficientes sobre el conjunto permitido de permisos. El evento de creación de nuevo usuario se capturaría en el Registro de Eventos."
    }
  ],
  "lastModified": "2026-06-17T03:37:24.067",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:google:exposure_notifications_verification_server:*:*:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "4AB50BC0-EC62-473B-8550-917FB077D093",
              "versionEndExcluding": "0.23.1"
            }
          ],
          "operator": "OR"
        }
      ]
    }
  ],
  "sourceIdentifier": "cve-coordination@google.com"
}