CVE-2004-1008 in PuTTY
Summary
by MITRE
Integer signedness error in the ssh2_rdpkt function in PuTTY before 0.56 allows remote attackers to execute arbitrary code via a SSH2_MSG_DEBUG packet with a modified stringlen parameter, which leads to a buffer overflow.
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Analysis
by VulDB Data Team • 06/30/2019
The vulnerability identified as CVE-2004-1008 represents a critical integer signedness error within the ssh2_rdpkt function of PuTTY versions prior to 0.56. This flaw exists in the Secure Shell protocol implementation and specifically targets the handling of SSH2_MSG_DEBUG packets. The vulnerability stems from improper validation of the stringlen parameter within the debug message processing routine, creating a scenario where an attacker can manipulate packet structures to trigger unintended behavior. The issue manifests when the application processes a malformed SSH2_MSG_DEBUG packet containing a modified stringlen field that exceeds expected boundaries, ultimately leading to a buffer overflow condition.
The technical implementation of this vulnerability involves a classic integer overflow scenario where the signedness of an integer parameter is incorrectly handled during buffer allocation calculations. When PuTTY processes the debug message packet, it uses the stringlen parameter to determine buffer size requirements without proper validation of the parameter's signedness. This allows an attacker to craft a packet where the stringlen value, when interpreted as a signed integer, can be manipulated to create a negative buffer size or cause integer overflow during arithmetic operations. The resulting buffer overflow occurs when the application attempts to allocate memory or copy data based on the manipulated length parameter, leading to memory corruption that can be exploited to execute arbitrary code.
From an operational impact perspective, this vulnerability presents a severe threat to SSH infrastructure security as it allows remote code execution without requiring authentication. Attackers can exploit this weakness by establishing an SSH connection to a vulnerable PuTTY client and sending a specially crafted debug packet. The exploitability is enhanced by the fact that the vulnerability does not require any form of authentication, making it particularly dangerous in environments where SSH clients are exposed to untrusted networks. The buffer overflow can potentially be leveraged to overwrite critical memory locations, including return addresses, function pointers, or other program state information, enabling attackers to redirect program execution flow and execute malicious code with the privileges of the affected process.
The vulnerability aligns with CWE-190, which describes integer overflow and underflow conditions, and specifically relates to CWE-121, which covers stack-based buffer overflow scenarios. Additionally, this weakness can be mapped to ATT&CK technique T1059, which covers command and scripting interpreter usage, as successful exploitation would likely involve executing arbitrary code through the compromised SSH client. The vulnerability also corresponds to ATT&CK technique T1133, representing external remote services, as it enables attackers to exploit SSH clients remotely without requiring local access. Organizations using vulnerable PuTTY versions face significant risk of unauthorized access to systems, data exfiltration, and potential lateral movement within networks where SSH clients are deployed.
Mitigation strategies for CVE-2004-1008 primarily involve immediate upgrade to PuTTY version 0.56 or later, which contains the necessary patches to address the integer signedness error. System administrators should implement network segmentation to limit exposure of SSH clients to untrusted networks and consider implementing network monitoring to detect anomalous SSH packet patterns. Additional protective measures include enabling SSH host key verification, implementing strict access controls, and conducting regular security assessments of SSH implementations. The vulnerability underscores the importance of proper input validation and integer handling in cryptographic software implementations, particularly in security-critical applications where buffer overflows can lead to complete system compromise. Organizations should also implement automated patch management processes to ensure timely deployment of security updates and maintain inventory of all SSH client installations across their infrastructure.