CVE-2004-1440 in PuTTY
Summary
by MITRE
Multiple heap-based buffer overflows in the modpow function in PuTTY before 0.55 allow (1) remote attackers to execute arbitrary code via an SSH2 packet with a base argument that is larger than the mod argument, which causes the modpow function to write memory before the beginning of its buffer, and (2) remote malicious servers to cause a denial of service (client crash) and possibly execute arbitrary code via a large bignum during authentication.
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Analysis
by VulDB Data Team • 06/29/2019
The vulnerability identified as CVE-2004-1440 represents a critical heap-based buffer overflow in the modpow function within PuTTY versions prior to 0.55. This flaw exists within the cryptographic implementation responsible for modular exponentiation operations during SSH2 protocol communication. The issue manifests when processing SSH2 packets where the base argument exceeds the modulus argument, creating a condition where the modpow function attempts to write data to memory locations before the allocated buffer boundaries. This fundamental memory corruption vulnerability presents significant security implications as it can be exploited by remote attackers to execute arbitrary code on vulnerable systems. The vulnerability is classified under CWE-121 as a heap-based buffer overflow, which occurs when a program writes data beyond the allocated memory space, potentially leading to code execution or system compromise.
The technical exploitation of this vulnerability involves two distinct attack vectors that leverage the same underlying buffer overflow condition. The first vector allows remote attackers to execute arbitrary code by crafting SSH2 packets with malformed base arguments that are larger than the modulus values. This specific condition causes the modpow function to perform memory writes before the buffer's beginning, creating a predictable memory corruption pattern that can be leveraged for code execution. The second vector targets the SSH client authentication process where malicious servers can trigger denial of service conditions through large bignum values during authentication, potentially leading to client crashes and in some cases, arbitrary code execution. Both attack scenarios exploit the same fundamental flaw in the cryptographic library implementation within PuTTY's SSH2 client functionality.
The operational impact of CVE-2004-1440 extends beyond simple exploitation to encompass broader security implications for SSH infrastructure. Systems utilizing vulnerable PuTTY versions face potential compromise through remote code execution attacks, particularly in environments where SSH clients connect to untrusted servers. The vulnerability affects the integrity of SSH communications and can lead to complete system compromise when successfully exploited. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1021.004 for remote service access and T1059 for command execution, as it enables adversaries to gain unauthorized access and execute commands on target systems. The vulnerability's impact is particularly severe because it affects the core cryptographic operations that secure SSH communications, undermining the fundamental security guarantees that SSH protocol implementations are designed to provide.
Mitigation strategies for CVE-2004-1440 require immediate patching of PuTTY installations to versions 0.55 or later where the buffer overflow has been addressed. System administrators should prioritize updating all SSH clients, particularly those running vulnerable PuTTY versions, to prevent exploitation. Network segmentation and firewall rules can provide additional defense-in-depth measures by restricting SSH access to trusted networks. Monitoring for suspicious SSH traffic patterns and anomalous authentication attempts can help detect exploitation attempts. The vulnerability demonstrates the importance of proper input validation in cryptographic implementations and highlights the need for thorough security testing of cryptographic libraries. Organizations should implement regular security assessments of their SSH infrastructure and maintain up-to-date cryptographic libraries to prevent similar vulnerabilities from being exploited in the future. Additionally, implementing intrusion detection systems that can identify malformed SSH packets and buffer overflow patterns can provide early warning of potential exploitation attempts.