{"id":"CVE-2026-63567","title":"Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc","summary":"Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who has captured an IES or ECIES ciphertext, and who can submit modified ciphertexts for decryption unde…","severity":"high","cvss":8.2,"cvssVector":"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","cwe":["CWE-203"],"vendor":"Legion of the Bouncy Castle Inc.","product":"BouncyCastle.Cryptography","affected":["BouncyCastle.Cryptography < 2.7.0"],"published":"2026-10-02","updated":"2026-10-02","sourceUpdated":"2026-10-02T07:16:37.127","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-63567","references":[{"url":"https://github.com/bcgit/bc-csharp/commit/eaa42e1e8125b3e2e25e365c4194c7cd5932360b","label":"91579145-5d7b-4cc5-b925-a0262ff19630"},{"url":"https://github.com/bcgit/bc-csharp/commit/f881400b761134160ec2a05fd27c3e569453788d","label":"91579145-5d7b-4cc5-b925-a0262ff19630"},{"url":"https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63567","label":"91579145-5d7b-4cc5-b925-a0262ff19630"}],"tags":["nvd","cve.org"],"cvssSource":"cna","ingestedAt":"2026-10-02T07:13:06.668Z","slug":"CVE-2026-63567","body":"## Overview\n\nObservable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who has captured an IES or ECIES ciphertext, and who can submit modified ciphertexts for decryption under the same key pair, to recover its plaintext via a CBC padding-oracle attack, because in block-cipher mode the engine decrypts the ciphertext and removes its padding before verifying the MAC. A padding failure is therefore reported with a different error message, and without the MAC computation, compared with a MAC failure. Only applications that construct IesEngine directly with a padded block cipher, such as AES in CBC mode with PKCS#7 padding, are affected; stream-mode IES is not.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":45,"depthScoreParts":{"impact":45.1,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}