{"id":"CVE-2026-15999","summary":"AES-CCM decryption accepts zero or out-of-range tag length, bypassing authentication","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.","modified":"2026-10-04T02:46:51.811836040Z","published":"2026-10-02T06:52:16.792Z","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"},"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"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/bcgit/bc-csharp","events":[{"introduced":"0"},{"fixed":"4007498b13582d90ee1eda5d9920c324428b98b3"},{"fixed":"2818bdfa55efd58b0d6a1c75f360b8404d879780"},{"fixed":"9d284d8f379614def853b590c62bbb31c48f7af0"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"2.7.0"}],"source":["DESCRIPTION","REFERENCES"]}}],"versions":["release-1.9.0","release-1.8.10","release-1.8.8","release-1.8.7","release-1.8.6","release-1.8.5","release-1.8.4","release-1.8.3","release-1.8.2","release-1.8.1","release-1.8.0","release-1.8.0-RC.3","release-1.8.0-RC.2","release-1.8.0-RC.1","release-1.8.0-beta.4","release-1.8.0-beta.3","release-1.8.0-beta.2","release-1.8.0-beta.1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-15999.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","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"}]}