CVE-2016-9433 in w3m
Summary
by MITRE
An issue was discovered in the Tatsuya Kinoshita w3m fork before 0.5.3-31. w3m allows remote attackers to cause a denial of service (out-of-bounds array access) via a crafted HTML page.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-9433 represents a critical out-of-bounds array access flaw within the w3m web browser implementation developed by Tatsuya Kinoshita. This issue affects versions prior to 0.5.3-31 and demonstrates how seemingly benign web content can be weaponized to disrupt system operations. The vulnerability resides in the HTML parsing and rendering components of the w3m browser, specifically in how it handles array indexing during document processing. When a maliciously crafted HTML page is loaded, the browser's memory management fails to properly validate array bounds, leading to unauthorized memory access patterns that can result in application crashes or system instability.
The technical exploitation of this vulnerability follows a classic buffer over-read pattern that aligns with CWE-125, which describes out-of-bounds read conditions in software implementations. Attackers can construct HTML documents containing malformed array references or excessive array indexing that bypass normal input validation mechanisms. The w3m browser's HTML parser processes these elements without adequate boundary checks, causing the application to access memory locations beyond the allocated array boundaries. This type of flaw typically occurs when developers assume certain array dimensions or when input validation fails to account for maliciously constructed data structures. The vulnerability demonstrates poor defensive programming practices where input data from untrusted sources is not sufficiently sanitized before array operations are performed.
From an operational perspective, this vulnerability creates significant risk for users who may encounter malicious web content during routine browsing activities. The denial of service impact means that legitimate users can be disrupted by simply visiting compromised websites or clicking on malicious links. The attack vector is particularly concerning because it requires no user interaction beyond normal web browsing behavior, making it a passive threat that can affect users across different operating systems and environments where w3m is installed. Organizations relying on w3m for web content viewing, automated testing, or embedded systems face potential service interruptions that could impact productivity or system availability. The vulnerability also represents a potential stepping stone for more sophisticated attacks, as initial compromise through denial of service can provide attackers with opportunities to establish persistence or escalate privileges.
The remediation for CVE-2016-9433 requires immediate patching of affected w3m installations to version 0.5.3-31 or later, which includes proper array boundary validation and input sanitization measures. System administrators should prioritize this update across all environments where w3m is deployed, particularly in automated systems or environments where users may encounter untrusted web content. Additional mitigations include implementing web content filtering solutions, deploying network-based intrusion detection systems to monitor for exploitation attempts, and establishing secure browsing policies that limit exposure to potentially malicious content. Security teams should also consider implementing application whitelisting controls to restrict execution of vulnerable w3m versions in enterprise environments. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how client-side vulnerabilities can be leveraged for broader operational disruption. Organizations should conduct vulnerability assessments to identify all systems running affected w3m versions and establish monitoring procedures to detect potential exploitation attempts.