CVE-2026-63567

Name of the Vulnerable Software and Affected Versions bc-csharp versions prior to 2.7.0

Description A discrepancy in the DecryptBlock() function of the IesEngine allows a remote attacker to recover plaintext from captured IES or ECIES ciphertexts. This occurs when an attacker submits modified ciphertexts for decryption using the same key pair, enabling a CBC padding-oracle attack. In block-cipher mode, the engine decrypts the ciphertext and removes padding before verifying the Message Authentication Code (MAC). Consequently, the system returns different error messages for padding failures versus MAC failures. This issue specifically affects applications that construct IesEngine directly with a padded block cipher, such as AES in CBC mode with PKCS#7 padding; stream-mode IES is not affected.

Recommendations Update bc-csharp to version 2.7.0 or later.