CVE-2024-31497

In PuTTY 0.68 through 0.80 before 0.81, biased ECDSA nonce generation
allows an attacker to recover a user’s NIST P-521 secret key via a quick
attack in approximately 60 signatures. This is especially important in a
scenario where an adversary is able to read messages signed by PuTTY or
Pageant. The required set of signed messages may be publicly readable
because they are stored in a public Git service that supports use of SSH
for commit signing, and the signatures were made by Pageant through an
agent-forwarding mechanism. In other words, an adversary may already have
enough signature information to compromise a victim’s private key, even if
there is no further use of vulnerable PuTTY versions. After a key
compromise, an adversary may be able to conduct supply-chain attacks on
software maintained in Git. A second, independent scenario is that the
adversary is an operator of an SSH server to which the victim authenticates
(for remote login or file copy), even though this server is not fully
trusted by the victim, and the victim uses the same private key for SSH
connections to other services operated by other entities. Here, the rogue
server operator (who would otherwise have no way to determine the victim’s
private key) can derive the victim’s private key, and then use it for
unauthorized access to those other services. If the other services include
Git services, then again it may be possible to conduct supply-chain attacks
on software maintained in Git. This also affects, for example, FileZilla
before 3.67.0, WinSCP before 6.3.3, TortoiseGit before 2.15.0.1, and
TortoiseSVN through 1.14.6.