{"id":"CVE-2026-103601","state":"PUBLISHED","title":"CcmBlockCipher and KCcmBlockCipher leave unverified plaintext in the output buffer after a failed tag check","description":"Release of unverified plaintext in the CCM (CcmBlockCipher) and DSTU 7624 CCM (KCcmBlockCipher) AEAD modes in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker to obtain decryptions of ciphertexts of their choosing via forged messages sent to an application that lets the output buffer of a failed decryption be observed, for example through buffer reuse or logging, because decryption wrote the recovered plaintext into the caller-supplied output buffer before checking the authentication tag and left it there when the check failed. Only decryption into a caller-supplied buffer is affected; methods that return a newly allocated array are not.","publishedAt":"2026-10-02T07:09:17.064Z","updatedAt":"2026-10-02T17:52:45.900Z","severity":{"score":8.2,"label":"High","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N","source":"bcorg"},"assigner":"bcorg","products":["Legion of the Bouncy Castle Inc. bc-csharp"],"affected":[{"vendor":"Legion of the Bouncy Castle Inc.","product":"bc-csharp","packageName":"BouncyCastle.Cryptography","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"2.7.0","versionType":"semver"}],"collectionURL":"https://www.nuget.org/packages/BouncyCastle.Cryptography","repo":"https://github.com/bcgit/bc-csharp","programFiles":["crypto/src/crypto/modes/CcmBlockCipher.cs","crypto/src/crypto/modes/KCcmBlockCipher.cs"]}],"references":["https://github.com/bcgit/bc-csharp/wiki/CVE-2026-103601","https://github.com/bcgit/bc-csharp/commit/e0868323645a063cb2479646e93c1449dc338de5","https://github.com/bcgit/bc-csharp/commit/4ddb1d0bfeae3a81b18f4446d8cc8a7871bd2d9f"],"weaknesses":["CWE-354"],"ingestedAt":"2026-10-29T20:10:23.711Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/103xxx/CVE-2026-103601.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-103601","state":"PUBLISHED","datePublished":"2026-10-02T07:09:17.064Z","dateUpdated":"2026-10-02T17:52:45.900Z","assignerShortName":"bcorg","assignerOrgId":"91579145-5d7b-4cc5-b925-a0262ff19630","dateReserved":"2026-09-30T23:01:10.053Z"},"containers":{"cna":{"title":"CcmBlockCipher and KCcmBlockCipher leave unverified plaintext in the output buffer after a failed tag check","descriptions":[{"lang":"en","value":"Release of unverified plaintext in the CCM (CcmBlockCipher) and DSTU 7624 CCM (KCcmBlockCipher) AEAD modes in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker to obtain decryptions of ciphertexts of their choosing via forged messages sent to an application that lets the output buffer of a failed decryption be observed, for example through buffer reuse or logging, because decryption wrote the recovered plaintext into the caller-supplied output buffer before checking the authentication tag and left it there when the check failed. Only decryption into a caller-supplied buffer is affected; methods that return a newly allocated array are not."}],"affected":[{"vendor":"Legion of the Bouncy Castle Inc.","product":"bc-csharp","packageName":"BouncyCastle.Cryptography","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"2.7.0","versionType":"semver"}],"collectionURL":"https://www.nuget.org/packages/BouncyCastle.Cryptography","repo":"https://github.com/bcgit/bc-csharp","programFiles":["crypto/src/crypto/modes/CcmBlockCipher.cs","crypto/src/crypto/modes/KCcmBlockCipher.cs"]}],"references":[{"url":"https://github.com/bcgit/bc-csharp/wiki/CVE-2026-103601","tags":["vendor-advisory"]},{"url":"https://github.com/bcgit/bc-csharp/commit/e0868323645a063cb2479646e93c1449dc338de5","tags":["patch"]},{"url":"https://github.com/bcgit/bc-csharp/commit/4ddb1d0bfeae3a81b18f4446d8cc8a7871bd2d9f","tags":["patch"]}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"HIGH","subConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","subIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED","version":"4.0","baseSeverity":"HIGH","baseScore":8.2,"vectorString":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-354","lang":"en","description":"CWE-354 Improper Validation of Integrity Check Value","type":"CWE"}]}],"providerMetadata":{"shortName":"bcorg","orgId":"91579145-5d7b-4cc5-b925-a0262ff19630","dateUpdated":"2026-10-02T07:09:17.064Z"},"impacts":[{"descriptions":[{"lang":"en","value":"Confidentiality (unverified plaintext left in the caller's buffer after a failed tag check, giving a CTR decryption oracle)"}]}],"credits":[{"lang":"en","value":"Discovered by Claude, Anthropic's AI assistant, and triaged by the Anthropic security team in collaboration with Anthropic Research.","type":"finder"}],"source":{"discovery":"EXTERNAL"},"x_generator":{"engine":"Claude Opus 5.5"},"x_antReportIds":["ANT-2026-A41MAVE2"]},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-02T17:50:08.465930Z","id":"CVE-2026-103601","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-02T17:52:45.900Z"}}]}}}