{"id":"CVE-2026-63573","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-63573","generatedAt":"2026-10-28T04:15:09.207Z","title":"Observable discrepancy in the CMS RSA PKCS#1 v1.5 key-transport unwrap (KeyTransRecipientInformation.UnwrapKey) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who holds a captured CMS EnvelopedData message, and who…","description":"Observable discrepancy in the CMS RSA PKCS#1 v1.5 key-transport unwrap (KeyTransRecipientInformation.UnwrapKey) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who holds a captured CMS EnvelopedData message, and who can submit many modified messages to an application that decrypts them with the recipient's RSA private key and reveals how decryption failed, to recover the captured message's content-encryption key and so its content, via a Bleichenbacher-style adaptive chosen-ciphertext attack, because a key-transport ciphertext with invalid PKCS#1 v1.5 padding is rejected during unwrap with a distinct \"bad padding in message.\" CmsException instead of being replaced by a random key, so it can be told apart from a correctly padded ciphertext, which fails only later at content decryption.","published":"2026-10-02T08:17:02.000Z","lastModified":"2026-10-02T20:17:03.000Z","status":"Undergoing Analysis","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:H/VI:N/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-203"],"affected":[],"epss":{"score":0.00308,"percentile":0.2345,"date":"2026-10-27","history":[{"date":"2026-10-02","score":0.00308,"percentile":0.21395}]},"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 (0.31%). 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":"2026-10-02T08:17:02.000Z","detail":{"score":"8.2","severity":"HIGH","publishedAt":"2026-10-02T08:17:02.317Z"},"summary":"New CVE, high severity (CVSS 8.2)."}],"references":[{"url":"https://github.com/bcgit/bc-csharp/commit/85679cc7023adf4e2a0650b88a1f4f98679c7463","source":"91579145-5d7b-4cc5-b925-a0262ff19630"},{"url":"https://github.com/bcgit/bc-csharp/commit/c38b4790e2aef68f116a551f73b94ea05cb5590c","source":"91579145-5d7b-4cc5-b925-a0262ff19630"},{"url":"https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63573","source":"91579145-5d7b-4cc5-b925-a0262ff19630"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-63573","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."}