Threats Tagged 'cve-2026-63573'

A vulnerability in Legion of the Bouncy Castle Inc. bc-csharp before version 2.7.0 allows a remote attacker to recover the content-encryption key of a captured CMS EnvelopedData message. This is due to an observable discrepancy in the RSA PKCS#1 v1.5 key-transport unwrap process, where invalid padding errors are distinguishable from other decryption failures. This enables a Bleichenbacher-style adaptive chosen-ciphertext attack.

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.