Crypt::DSA versions before 1.22 for Perl draw the DSA signing nonce and private key from a biased random generator, leading to private-key recovery.
“Crypt::DSA::Util::makerandom forces the high bit of every value it returns to obtain an exactly N-bit integer for prime search. The signing nonce and the private key are drawn from makerandom. Because the high bit is always set, the result is not uniform: its top bit is fixed, producing insecure values.”
An attacker who collects a modest number of signatures under an affected key, together with the public key, can recover the private key with a lattice attack.
Keys used to sign with an affected version should be considered compromised and new keys should be generated.
