The ElGamal implementation in Crypto++ through 8.5 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.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-40530
• https://eprint.iacr.org/2021/923
• 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
• https://lists.fedoraproject.org/archives/list/[email protected]/message/57OJA2K5AHX5HAU2QBDRWLGIIUX7GASC/
• https://lists.fedoraproject.org/archives/list/[email protected]/message/HGVBZ2TTRKCTYAZTRHTF6OBD4W37F5MT/
• https://lists.fedoraproject.org/archives/list/[email protected]/message/VJYOZGWI7TD27SEXILSM6VUTPPEICDL7/