Secret key recovery of NIST P-521 private keys in PuTTY

1) Cryptographic issues

EUVDB-ID: #VU88542

Risk: Medium

CVSSv3.1: 5.3 [CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N/E:P/RL:O/RC:C]

CVE-ID: CVE-2024-31497

CWE-ID: CWE-310 - Cryptographic Issues

Exploit availability: Yes

Description

The vulnerability allows a remote attacker to recover NIST P-521 private keys.

The vulnerability exists due to the PuTTY client and all related components generate heavily biased ECDSA nonces in the case of NIST P-521. A remote attacker can recover the NIST P-521 private key using roughly 60 valid ECDSA signatures generated by any PuTTY component under the same key.

Note, if the key has been used to sign arbitrary data (e.g., git commits by forwarding Pageant to a development host), the publicly available signatures (e.g., on GitHub) can be used as well.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

PuTTY: 0.68 - 0.80

External links

http://seclists.org/oss-sec/2024/q2/122

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.