{"id":"CVE-2026-15999","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-15999","generatedAt":"2026-10-28T05:59:52.318Z","title":"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…","description":"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.","published":"2026-10-02T07:16:36.000Z","lastModified":"2026-10-27T16:34:54.000Z","status":"Analyzed","sourceIdentifier":"91579145-5d7b-4cc5-b925-a0262ff19630","cvss":{"version":"4.0","score":8.2,"severity":"HIGH","vector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M"},"cwe":["CWE-354"],"affected":["bouncycastle/bc-csharp"],"epss":{"score":0.00261,"percentile":0.17784,"date":"2026-10-27","history":[{"date":"2026-10-02","score":0.00227,"percentile":0.12222}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.26%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"new","label":"New CVE","at":"2026-10-02T07:16:36.000Z","detail":{"score":"8.2","severity":"HIGH","publishedAt":"2026-10-02T07:16:36.193Z"},"summary":"New CVE, high severity (CVSS 8.2)."}],"references":[{"url":"https://github.com/bcgit/bc-csharp/commit/2818bdfa55efd58b0d6a1c75f360b8404d879780","tags":["Patch"],"source":"91579145-5d7b-4cc5-b925-a0262ff19630"},{"url":"https://github.com/bcgit/bc-csharp/commit/9d284d8f379614def853b590c62bbb31c48f7af0","tags":["Patch"],"source":"91579145-5d7b-4cc5-b925-a0262ff19630"},{"url":"https://github.com/bcgit/bc-csharp/wiki/CVE-2026-15999","tags":["Patch","Vendor Advisory"],"source":"91579145-5d7b-4cc5-b925-a0262ff19630"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-15999","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}