PuTTY Vulnerable to Private Key Compromise Attack

Summary

PuTTY, a popular SSH and Telnet client, is currently subject to a vulnerability that can allow an attacker to compromise private keys. This vulnerability, identified as CVE-2024-31497 (CVSSv3: 5.9), affects 521-bit ECSA keys, and allows an attacker to recover a user’s NIST P-521 secret key utilizing a quick attack in roughly 60 signatures. The attacker, after compromising the private key, can log into any service for which that key is used.

Impact Assessment

This vulnerability can only compromise private keys when the key type is 521-bit ECDSA. If your organization does not utilize this key type, it is not subject to this vulnerability.

Affected Software:

• PuTTy Secure Shell (SSH) (0.68-0.80)
• FileZilla (3.24.1 - 3.66.5)
• WinSCP (5.9.5 - 6.3.2)
• TortoiseGit (2.4.0.2 - 2.15.0)
• TortoiseSVN (1.10.0 - 1.14.6)

What It Means for You

If you or your organization utilize PuTTY and 521-bit ECDSA keys, changing key types or performing a patch is essential for remediation.

Remediation

1. Updating to version .81 of PuTTY will remediate this vulnerability.
2. Updating any version after the following versions will remediate the other affected software, FileZilla 3.67.0, WinSCP 6.3.3, TortoiseGit 2.15.0.1, and TortoiseSVN 1.14.6.

Mitigation

Utilizing another key type other than 521-bit ECDSA keys will mitigate this vulnerability.

Business Implications

Exploitation of this vulnerability can allow an attacker to access/interact with any services that utilize the compromised key and the consequences depend entirely on which services use the compromised key. Denial of service and unauthorized access to services are likely consequences, which can cause business inefficiencies and require an incident response effort.

Access Point Consulting Recommends

1. Patch: Patching this vulnerability is the easiest way to perform mitigation.
2. Mitigate: If utilizing the 521-bit ECDSA key, it is possible to mitigate this vulnerability by discontinuing use of that key type.
3. Generate new keys: If your organization has updated to a non-vulnerable version of PuTTY it is recommended to also generate new keys as it is possible they could already be compromised.

Associated Bulletins

PuTTY SSH client flaw allows recovery of cryptographic private keys (bleepingcomputer.com)

CVE-2024-31497 | Tenable®

NVD - CVE-2024-31497 (nist.gov)

Widely-Used PuTTY SSH Client Found Vulnerable to Key Recovery Attack (thehackernews.com)

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