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CVE-2016-4028

Status: ModifiedHigh (7.5)—

An issue was discovered in Open-Xchange OX Guard before 2.4.0-rev8. OX Guard uses an authentication token to identify and transfer guest users' credentials. The OX Guard API acts as a padding oracle by responding with different error codes depending on whether the provided token matches the encryption padding. In combination with AES-CBC, this allows attackers to guess the correct padding. Attackers may run brute-forcing attacks on the content of the guest authentication token and discover user credentials. For a practical attack vector, the guest users needs to have logged in, the content of the guest user's "OxReaderID" cookie and the value of the "auth" parameter needs to be known to the attacker.

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)

Open-xchange — OX Guard

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2016-4028",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 3.5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:M/Au:S/C:P/I:N/A:N",
          "authentication": "SINGLE",
          "integrityImpact": "NONE",
          "accessComplexity": "MEDIUM",
          "availabilityImpact": "NONE",
          "confidentialityImpact": "PARTIAL"
        },
        "acInsufInfo": false,
        "impactScore": 2.9,
        "baseSeverity": "LOW",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 6.8,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": false
      }
    ],
    "cvssMetricV30": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.0",
          "baseScore": 7.5,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "HIGH",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 1.6
      }
    ]
  },
  "affected": [
    {
      "source": "cve@mitre.org",
      "affectedData": [
        {
          "vendor": "n/a",
          "product": "n/a",
          "versions": [
            {
              "status": "affected",
              "version": "n/a"
            }
          ]
        }
      ]
    }
  ],
  "published": "2016-12-15T06:59:07.457",
  "references": [
    {
      "url": "http://www.securityfocus.com/archive/1/538732/100/0/threaded",
      "source": "cve@mitre.org"
    },
    {
      "url": "http://www.securitytracker.com/id/1036154",
      "tags": [
        "Third Party Advisory",
        "VDB Entry"
      ],
      "source": "cve@mitre.org"
    },
    {
      "url": "http://www.securityfocus.com/archive/1/538732/100/0/threaded",
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "http://www.securitytracker.com/id/1036154",
      "tags": [
        "Third Party Advisory",
        "VDB Entry"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-255"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "An issue was discovered in Open-Xchange OX Guard before 2.4.0-rev8. OX Guard uses an authentication token to identify and transfer guest users' credentials.  The OX Guard API acts as a padding oracle by responding with different error codes depending on whether the provided token matches the encryption padding.  In combination with AES-CBC, this allows attackers to guess the correct padding.  Attackers may run brute-forcing attacks on the content of the guest authentication token and discover user credentials.  For a practical attack vector, the guest users needs to have logged in, the content of the guest user's \"OxReaderID\" cookie and the value of the \"auth\" parameter needs to be known to the attacker."
    },
    {
      "lang": "es",
      "value": "Se descubrió un problema en OX Guard de Open-Xchange anterior a versión 2.4.0-rev8. OX Guard utiliza un token de autenticación para identificar y transferir las credenciales de usuarios invitados. La API de OX Guard actúa como un oráculo de relleno (padding oracle) al responder con diferentes códigos de error dependiendo de si el token provisto coincide con el cifrado de relleno (encryption padding). En combinación con AES-CBC, esto permite a los atacantes adivinar el relleno correcto. Los atacantes pueden ejecutar ataques violentos en el contenido del token de autenticación del invitado y detectar las credenciales del usuario. Para un vector de ataque práctico, los usuarios invitados necesitan haber iniciado sesión, el contenido de la cookie \"OxReaderID\" del usuario invitado y el valor del parámetro \"auth\" deben ser conocidos por el atacante."
    }
  ],
  "lastModified": "2026-06-17T00:46:45.600",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:open-xchange:ox_guard:*:rev7:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "C53D52F6-DBFF-4FCF-9EB7-B7537A32EFD5",
              "versionEndIncluding": "2.4.0"
            }
          ],
          "operator": "OR"
        }
      ]
    }
  ],
  "sourceIdentifier": "cve@mitre.org"
}