In Botan 1.8.0 through 1.11.33, when decoding BER data an integer overflow could occur, which would cause an incorrect length field to be computed. Some API callers may use the returned (incorrect and attacker controlled) length field in a way which later causes memory corruption or other failure.
Botan 1.11.x before 1.11.29 does not enforce TLS policy for (1) signature algorithms and (2) ECC curves, which allows remote attackers to conduct downgrade attacks via unspecified vectors.
Botan before 1.10.13 and 1.11.x before 1.11.29 do not use a constant-time algorithm to perform a modular inverse on the signature nonce k, which might allow remote attackers to obtain ECDSA secret keys via a timing side-channel attack.