cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing

{
  "id": "b26fe8723763708e8e7bd88c1b497d95016d61af8f06e06b84c24328781720bf",
  "url": "https://osv.dev/vulnerability/CVE-2026-69247",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing",
    "summary": "cryptography is a package designed to expose cryptographic primitives and recipes to Python developers. From 44.0.0 until 50.0.0, pkcs7_decrypt_der, pkcs7_decrypt_pem, and pkcs7_decrypt_smime reported the outcome of decrypting a RecipientInfo's encryptedKey in several distinguishable ways, one of which disclosed the exact length recovered from the RSA operation. The same distinction was also observable by timing. An application that decrypts attacker-supplied EnvelopedData and reflects the outcome gives the attacker a Bleichenbacher oracle against the content-encryption key. Decryption ran as RSA PKCS#1 v1.5 decrypt of encryptedKey, build an AES cipher from the result, then AES-CBC decrypt and PKCS#7 unpad. Invalid RSA padding, a valid padding with a bad key length, a correct length with a wrong key, and the real key each failed or succeeded differently. Case 1 is reachable only where the linked library lacks implicit rejection: OpenSSL 3.0 and 3.1, LibreSSL, and BoringSSL. Exploitation requires a service that auto-decrypts untrusted EnvelopedData matching the victim certificate and answers adaptively at high volume, such as an S/MIME gateway or mail filter. This issue is fixed in 50.0.0.",
    "evidence": "osv:CVE-2026-69247",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-69247",
      "aliases": [
        "CVE-2026-69247",
        "GHSA-g6cj-pr64-35w5",
        "PYSEC-2026-3552"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/pyca/cryptography",
              "type": "GIT",
              "events": [
                {
                  "introduced": "f299a48153650f2dd87716343f2daa7cd39a1f59"
                },
                {
                  "fixed": "dcb7050b807b00392fa9fe2eac7cb362fcf355cc"
                },
                {
                  "fixed": "53fccd93413a8d7f07d6d8999681f27b75cffa3f"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "44.0.0"
                      },
                      {
                        "fixed": "50.0.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "53fccd93413a8d7f07d6d8999681f27b75cffa3f"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "49.0.0",
            "48.0.0",
            "47.0.0",
            "46.0.1",
            "46.0.0",
            "45.0.0",
            "44.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-69247.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:22.686857240Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/69xxx/CVE-2026-69247.json",
        "https://github.com/pyca/cryptography/security/advisories/GHSA-g6cj-pr64-35w5",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-69247",
        "https://github.com/pyca/cryptography/commit/53fccd93413a8d7f07d6d8999681f27b75cffa3f",
        "https://github.com/pyca/cryptography/pull/15369"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-208",
          "CWE-209"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/69xxx/CVE-2026-69247.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-69247",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 489222,
  "published_at": "2026-08-03T21:16:32.047+00:00"
}