CVE-2005-2930 in Chm Lib
Summary
by MITRE
Stack-based buffer overflow in the _chm_find_in_PMGL function in chm_lib.c for chmlib before 0.36, as used in products such as KchmViewer, allows user-assisted attackers to execute arbitrary code via a CHM file containing a long element, a different vulnerability than CVE-2005-3318.
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Analysis
by VulDB Data Team • 07/06/2021
The vulnerability described in CVE-2005-2930 represents a critical stack-based buffer overflow flaw within the chmlib library version 0.35 and earlier, specifically within the _chm_find_in_PMGL function located in chm_lib.c. This library serves as a core component for handling Microsoft Compiled HTML Help (CHM) files, which are widely used documentation formats across various software applications. The flaw manifests when processing CHM files containing excessively long elements, creating a condition where attacker-controlled input can overwrite adjacent memory on the stack, potentially leading to arbitrary code execution. The vulnerability is particularly concerning because it operates through user-assisted attack vectors, meaning an attacker can craft a malicious CHM file that, when opened by an application using the vulnerable chmlib library, triggers the buffer overflow condition.
The technical implementation of this vulnerability stems from inadequate bounds checking within the _chm_find_in_PMGL function, which processes PMGL (Project Management Group List) structures found in CHM files. When the function encounters a particularly long element within the CHM's internal structure, it fails to properly validate the input length before copying data onto the stack. This classic stack-based buffer overflow occurs because the function uses a fixed-size buffer that cannot accommodate the oversized input, causing data to spill over into adjacent stack memory locations. The vulnerability is categorized under CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows that occur in stack-allocated memory regions. This flaw allows for potential exploitation through the overwrite of return addresses, function pointers, or other critical stack data, providing attackers with opportunities to redirect program execution flow.
The operational impact of CVE-2005-2930 extends beyond simple code execution, as it affects numerous applications that rely on chmlib for CHM file processing, including popular tools like KchmViewer and various other software packages that integrate CHM parsing capabilities. The user-assisted nature of this vulnerability means that successful exploitation requires an end-user to open a maliciously crafted CHM file, making it particularly dangerous in social engineering scenarios where users might encounter such files through email attachments, web downloads, or removable media. Applications that implement CHM parsing using vulnerable versions of chmlib become potential attack vectors for remote code execution, allowing adversaries to gain unauthorized access to systems, escalate privileges, or establish persistent backdoors. The vulnerability demonstrates the broader implications of library-level flaws, where a single security issue in a widely-used component can compromise numerous applications across different platforms and vendors.
Mitigation strategies for this vulnerability require immediate remediation through library updates to chmlib version 0.36 or later, which contains the necessary patches to prevent the buffer overflow condition. System administrators should conduct comprehensive inventory assessments to identify all applications utilizing vulnerable versions of chmlib, particularly those handling user-supplied CHM files or documentation. The implementation of input validation controls, such as length checking and sanitization of CHM file elements, can provide additional defense-in-depth measures, though these are secondary to the core library update. Security monitoring should include detection of suspicious CHM file access patterns and potential exploitation attempts, with network-based intrusion detection systems configured to identify malformed CHM content. This vulnerability aligns with ATT&CK technique T1203, which covers Exploitation for Client Execution, and demonstrates how vulnerabilities in common libraries can create widespread attack surface opportunities. Organizations should also consider implementing application whitelisting policies to restrict execution of untrusted CHM files and ensure that all systems processing such content are regularly updated to prevent exploitation of this and similar legacy vulnerabilities.