April 16, 2024 at 11:07AM
The PuTTY version 0.68 through 0.80 contains a vulnerability (CVE-2024-31497) that could allow attackers with access to 60 cryptographic signatures to recover the private key used for their generation. It affects systems using ECDSA keys and could be exploited to gain unauthorized access to SSH servers or sign commits as the developer. PuTTY version 0.81 fixes this flaw and introduces a new technique for key generation. Other impacted software includes FileZilla, WinSCP, TortoiseGit, and TortoiseSVN. Users are advised to update their tools to mitigate the risk.
Key takeaways from the meeting notes:
1. PuTTY vulnerability: The CVE-2024-31497 tracked vulnerability in PuTTY versions 0.68 through 0.80 could enable attackers with access to cryptographic signatures to recover the private key used for their generation. This poses a significant threat as PuTTY is frequently used by system administrators and developers for remote server and device management over SSH from Windows-based clients.
2. Vulnerability cause and impact: The vulnerability is caused by how PuTTY generates ECDSA nonces for the NIST P-521 curve used for SSH authentication, creating a bias due to deterministic generation of numbers to compensate for the lack of a robust cryptographic random number generator on specific Windows versions. Exploiting this vulnerability could lead to unauthorized access to SSH servers or signing commits as the developer.
3. Exploitation: Attackers require 58 signatures to calculate a target’s private key, which they can acquire from logins to compromised or controlled SSH servers or from signed Git commits. The technique of harvesting signatures from public commits is particularly practical for attackers and can be exploited without the need to compromise a server in advance.
4. Resolution: PuTTY version 0.81 fixed the vulnerability by switching to the RFC 6979 technique for all DSA and ECDSA keys. However, P521 private keys generated using the vulnerable version of PuTTY should be considered unsafe and replaced by new, secure keys. Other software impacted by the vulnerability includes FileZilla, WinSCP, TortoiseGit, and TortoiseSVN, depending on the PuTTY version they incorporate.
5. Recommendation: Users are advised to check their software tools for potential impact by CVE-2024-31497 and take preventive action as needed.
These key takeaways provide a clear understanding of the PuTTY vulnerability and its implications, as well as the necessary steps to address the issue.