CVE-2018-6197 in w3m
Summary
by MITRE
w3m through 0.5.3 is prone to a NULL pointer dereference flaw in formUpdateBuffer in form.c.
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Analysis
by VulDB Data Team • 02/02/2023
The vulnerability identified as CVE-2018-6197 affects the w3m web browser version 0.5.3 and earlier, presenting a critical NULL pointer dereference flaw within the formUpdateBuffer function located in the form.c source file. This issue represents a fundamental programming error that occurs when the software attempts to access a memory location through a pointer that has not been properly initialized or has been set to NULL. The flaw specifically manifests during form handling operations where the application fails to validate pointer references before dereferencing them, creating a potential crash condition that could be exploited by malicious actors.
The technical nature of this vulnerability aligns with CWE-476, which describes NULL pointer dereference conditions that occur when software attempts to access memory through a pointer that contains a NULL value. This particular implementation flaw exists in the form processing subsystem of w3m, which is commonly used as a text-based web browser in terminal environments and embedded systems. When a web page contains malformed form elements or specific input sequences, the formUpdateBuffer function fails to properly handle the absence of expected data structures, leading to an immediate crash of the application.
The operational impact of this vulnerability extends beyond simple application instability, as it can be leveraged for denial-of-service attacks against systems running vulnerable versions of w3m. Attackers could craft malicious web pages containing specially formatted forms that trigger the NULL pointer dereference when the browser attempts to process them, causing the application to terminate unexpectedly. This behavior creates a persistent threat to systems that rely on w3m for web browsing, particularly in environments where automated processes or embedded devices use this browser component. The vulnerability is particularly concerning in server environments where w3m might be used to fetch or process web content programmatically, as such crashes could be exploited to disrupt services or potentially escalate to more severe attacks.
Mitigation strategies for CVE-2018-6197 primarily involve upgrading to w3m version 0.5.4 or later, which contains the necessary patches to address the NULL pointer dereference issue. System administrators should also implement additional security controls such as input validation for web content and network segmentation to limit potential attack surfaces. The vulnerability demonstrates the importance of proper pointer validation and error handling in security-critical applications, aligning with ATT&CK technique T1499.004 for Network Denial of Service and emphasizing the need for robust software testing practices including static code analysis and dynamic testing to identify similar memory safety issues. Organizations should also consider implementing application whitelisting policies and monitoring for unusual application crash patterns that might indicate exploitation attempts against this or similar vulnerabilities.