CybserSecurity News

Tag: CVE-2024-31497

  • Citrix Warns: PuTTY Flaw Exposes XenCenter SSH Keys to Theft

    Citrix has issued a warning to its clients regarding the need for manual mitigation of a vulnerability in the SSH client PuTTY, which could allow malicious actors to steal the SSH private key of a XenCenter administrator.

    XenCenter is a tool for managing Citrix Hypervisor environments from a Windows desktop, including the deployment and monitoring of virtual machines.

    The vulnerability, identified as CVE-2024-31497, affects multiple versions of XenCenter for Citrix Hypervisor 8.2 CU1 LTSR that utilize PuTTY to establish SSH connections with guest virtual machines when using the “Open SSH Console” feature.

    Citrix Endpoint Management Vulnerability
    Citrix Systems Inc. / CC BY (https://creativecommons.org/licenses/by/3.0)

    Citrix has informed us that the third-party component PuTTY was removed in XenCenter version 8.2.6, and from version 8.2.7 onwards, it will no longer be included in XenCenter.

    The issue pertains to versions of PuTTY before 0.81: under certain scenarios, in conjunction with XenCenter, the vulnerability allows an attacker, who controls a guest virtual machine, to deduce the XenCenter administrator’s private SSH key, according to Citrix specialists.

    The vulnerability was discovered by Fabian Bömer and Markus Brinkmann from Ruhr University in Bochum. The flaw is attributed to older versions of the Windows-run PuTTY SSH client generating one-time ECDSA numbers (temporary unique cryptographic numbers) for the NIST P-521 curve used for authentication.

    To mitigate the vulnerability, Citrix recommends that administrators download the latest version of PuTTY and install it to replace the version included in older XenCenter releases.

    Clients who do not require the “Open SSH Console” functionality can completely remove the PuTTY component. Those wishing to continue using PuTTY should replace the installed version in the XenCenter system with an updated one, version number 0.81 or higher.

  • CVE-2024-31497: PuTTY Exploit Endangers Data

    The developers of PuTTY are issuing a warning about a critical vulnerability affecting versions 0.68 to 0.80, which could potentially allow an attacker to completely reconstruct private NIST-P521 keys.

    The vulnerability, identified as CVE-2024-31497, arises from failures in generating cryptographic nonces for ECDSA (Elliptic Curve Digital Signature Algorithm), enabling the recovery of private keys. The discovery of this flaw is attributed to researchers Fabian Bömer and Markus Brinkmann from Ruhr University Bochum.

    CVE-2024-31497

    The first 9 bits of each ECDSA nonce are set to zero, allowing the complete recovery of the secret key from approximately 60 signatures using state-of-the-art methods.

    An attacker in possession of several dozen signed messages and the public key would have sufficient data to recover the private key and forge signatures, potentially leading to unauthorized access to servers and services utilizing this key.

    The issue has also affected other products integrated with the vulnerable versions of PuTTY:

    • FileZilla (versions 3.24.1 – 3.66.5);
    • WinSCP (versions 5.9.5 – 6.3.2);
    • TortoiseGit (versions 2.4.0.2 – 2.15.0);
    • TortoiseSVN (versions 1.10.0 – 1.14.6).

    Following responsible disclosure, the issue was resolved in the newer versions of PuTTY 0.81, FileZilla 3.67.0, WinSCP 6.3.3, and TortoiseGit 2.15.0.1. The developers have employed RFC 6979 techniques for generating all types of DSA and ECDSA keys, abandoning the previous method.

    Users of TortoiseSVN are advised to use Plink from the latest PuTTY release, version 0.81, for accessing SVN repositories via SSH until an update is released.

    ECDSA NIST-P521 keys used in any of the vulnerable components should be considered compromised and immediately revoked, removing them from “~/.ssh/authorized_keys” and similar files on other SSH servers.