CVE-2021-40529 (https://ibm.github.io/system-security-research-updates/2021/07/20/insecurity-elgamal-pt1, https://ibm.github.io/system-security-research-updates/2021/09/06/insecurity-elgamal-pt2):
The ElGamal implementation in Botan through 2.18.1, as used in Thunderbird and other products, allows plaintext recovery because, during interaction between two cryptographic libraries, a certain dangerous combination of the prime defined by the receiver's public key, the generator defined by the receiver's public key, and the sender's ephemeral exponents can lead to a cross-configuration attack against OpenPGP.
Unreleased patch: https://github.com/randombit/botan/pull/2790
I'm sorry, this was fixed in 2.18.2.
sorry, forgot about this bug: https://github.com/gentoo/gentoo/commit/b4c6d315ef4456f223851a4aeee6892d26571a32