Message Authentication Key Exposure in IesEngine of Legion of the Bouncy Castle Inc.

CVE-2026-16001

What is CVE-2026-16001?

The IesEngine in the bc-csharp library prior to version 2.7.0 is susceptible to a vulnerability where the message authentication key is exposed through the encryption keystream. A remote attacker can exploit this weakness by observing an encrypted message that contains known plaintext. This allows the attacker to forge valid messages by manipulating the ciphertext and the MAC tag. The vulnerability arises because the MAC key, derived from the key generation process, can be extracted directly after the keystream, within the length of the message, compromising the integrity of the authentication and potentially leading to unauthorized actions.

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