{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "2.7.0"
              }
            ],
            "source": [
              "DESCRIPTION",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4007498b13582d90ee1eda5d9920c324428b98b3"
            },
            {
              "fixed": "2818bdfa55efd58b0d6a1c75f360b8404d879780"
            },
            {
              "fixed": "9d284d8f379614def853b590c62bbb31c48f7af0"
            }
          ],
          "repo": "https://github.com/bcgit/bc-csharp",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "bcorg",
    "cwe_ids": [
      "CWE-354"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/15xxx/CVE-2026-15999.json"
  },
  "details": "Improper validation of integrity check value in the AES-CCM implementation (CcmParameters and CcmBlockCipher) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an on-path attacker to modify CCM-encrypted content without detection via an AlgorithmIdentifier whose CCMParameters declare an authentication tag (aes-ICVlen) of zero or another length outside the RFC 5084 set, because CcmParameters accepted any value and CcmBlockCipher validated the tag length only when encrypting, so decryption compared a zero-length or very short tag. Affected paths include ParameterUtilities.GetCipherParameters, used by CmsEnvelopedData and CmsEnvelopedDataParser for EnvelopedData encrypted with AES-CCM, and any caller passing an unchecked tag length to CcmBlockCipher for decryption.",
  "id": "CVE-2026-15999",
  "modified": "2026-10-04T02:30:25.522100377Z",
  "published": "2026-10-02T06:52:16.792Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://www.nuget.org/packages/BouncyCastle.Cryptography"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/15xxx/CVE-2026-15999.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/bcgit/bc-csharp/wiki/CVE-2026-15999"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-15999"
    },
    {
      "type": "FIX",
      "url": "https://github.com/bcgit/bc-csharp/commit/2818bdfa55efd58b0d6a1c75f360b8404d879780"
    },
    {
      "type": "FIX",
      "url": "https://github.com/bcgit/bc-csharp/commit/9d284d8f379614def853b590c62bbb31c48f7af0"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/bcgit/bc-csharp"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "AES-CCM decryption accepts zero or out-of-range tag length, bypassing authentication"
}