CVE-2015-2157 in PuTTY
Summary
by MITRE
The (1) ssh2_load_userkey and (2) ssh2_save_userkey functions in PuTTY 0.51 through 0.63 do not properly wipe SSH-2 private keys from memory, which allows local users to obtain sensitive information by reading the memory.
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Analysis
by VulDB Data Team • 11/28/2024
The vulnerability CVE-2015-2157 affects PuTTY versions 0.51 through 0.63 and represents a critical memory handling flaw that compromises the security of SSH-2 private keys. This issue resides in the ssh2_load_userkey and ssh2_save_userkey functions within the PuTTY SSH client implementation, where sensitive cryptographic material is not properly cleared from memory after use. The flaw falls under CWE-16 Configuration, specifically addressing improper handling of sensitive data in memory, and aligns with ATT&CK technique T1552.001 Credential Access: Credentials In Files, as it enables unauthorized access to stored credentials through memory inspection techniques.
The technical implementation of this vulnerability stems from inadequate memory sanitization practices during key loading and saving operations. When PuTTY processes SSH-2 private keys, it fails to overwrite the memory regions containing the cryptographic material with zeros or random data before releasing them back to the system. This leaves remnants of the private key accessible to local processes that can perform memory dumps or direct memory reads. The vulnerability is particularly dangerous because it allows attackers to recover private keys even after the application has closed, as the memory pages containing the sensitive information may not have been properly cleared. This represents a classic case of insufficient data sanitization that violates fundamental security principles for handling cryptographic keys.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially compromise entire SSH infrastructure security. Local users with access to the system can exploit this weakness through various means including process memory inspection, core dump analysis, or direct memory access techniques. Attackers could leverage this vulnerability to gain unauthorized access to systems that rely on the affected PuTTY versions for SSH connections, particularly in environments where users store private keys in the application's memory. The implications are severe as compromised private keys can be used to authenticate to SSH servers, establish unauthorized connections, and potentially escalate privileges within the network. This vulnerability directly impacts the confidentiality and integrity of SSH communications and represents a significant risk to organizations relying on PuTTY for secure remote access.
Mitigation strategies for CVE-2015-2157 require immediate remediation through version upgrades to PuTTY 0.64 or later, where the memory handling has been properly addressed. Organizations should implement comprehensive memory sanitization practices for all cryptographic operations and ensure that sensitive data is properly cleared from memory before deallocation. System administrators should conduct thorough vulnerability assessments to identify all systems running affected PuTTY versions and implement mandatory patching schedules. Additional protective measures include monitoring for unauthorized memory access patterns, implementing proper access controls to limit local user privileges, and conducting regular security audits of cryptographic key management processes. The vulnerability also highlights the importance of following secure coding practices and proper memory management techniques, particularly when handling sensitive cryptographic information, as outlined in industry standards such as NIST SP 800-57 and ISO/IEC 27001 security controls for information security management.