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CVE-2021-34813

Status: ModifiedCritical (9.8)—

Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting to retrieve an Olm encrypted room key backup from the homeserver) because olm_pk_decrypt has a stack-based buffer overflow. Remote code execution might be possible for some nonstandard build configurations.

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)

Matrix — OLM

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-34813",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 7.5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:L/Au:N/C:P/I:P/A:P",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "LOW",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "PARTIAL"
        },
        "acInsufInfo": false,
        "impactScore": 6.4,
        "baseSeverity": "HIGH",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 10,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": false
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.8,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "cve@mitre.org",
      "affectedData": [
        {
          "vendor": "n/a",
          "product": "n/a",
          "versions": [
            {
              "status": "affected",
              "version": "n/a"
            }
          ]
        }
      ]
    }
  ],
  "published": "2021-06-16T18:15:09.730",
  "references": [
    {
      "url": "https://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901b",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ],
      "source": "cve@mitre.org"
    },
    {
      "url": "https://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3",
      "tags": [
        "Release Notes",
        "Vendor Advisory"
      ],
      "source": "cve@mitre.org"
    },
    {
      "url": "https://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolm",
      "tags": [
        "Exploit",
        "Patch",
        "Vendor Advisory"
      ],
      "source": "cve@mitre.org"
    },
    {
      "url": "https://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901b",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3",
      "tags": [
        "Release Notes",
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolm",
      "tags": [
        "Exploit",
        "Patch",
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting to retrieve an Olm encrypted room key backup from the homeserver) because olm_pk_decrypt has a stack-based buffer overflow. Remote code execution might be possible for some nonstandard build configurations."
    },
    {
      "lang": "es",
      "value": "Matrix libolm versiones anteriores a 3.2.3 permite a un homeserver de Matrix malicioso bloquear a un cliente (mientras intenta recuperar una copia de seguridad de la clave de la sala cifrada por Olm desde el homeserver) porque la función olm_pk_decrypt presenta un desbordamiento de búfer en la región stack de la memoria. Una ejecución de código remota podría ser posible para algunas configuraciones de construcción no estándar"
    }
  ],
  "lastModified": "2026-06-17T03:56:36.990",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:matrix:olm:*:*:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "20186CE3-75A8-4275-8CA1-709F930424B6",
              "versionEndExcluding": "3.2.3"
            }
          ],
          "operator": "OR"
        }
      ]
    }
  ],
  "sourceIdentifier": "cve@mitre.org"
}