CVE-2016-9426 in w3m
Summary
by MITRE
An issue was discovered in the Tatsuya Kinoshita w3m fork before 0.5.3-31. Integer overflow vulnerability in the renderTable function in w3m allows remote attackers to cause a denial of service (OOM) and possibly execute arbitrary code due to bdwgc's bug (CVE-2016-9427) via a crafted HTML page.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-9426 represents a critical integer overflow flaw within the w3m web browser fork developed by Tatsuya Kinoshita. This issue affects versions prior to 0.5.3-31 and demonstrates how seemingly minor implementation errors can lead to severe security consequences. The vulnerability specifically resides within the renderTable function, which is responsible for processing HTML table structures during web page rendering. When processing maliciously crafted HTML content, the function fails to properly validate integer values, creating conditions where arithmetic operations can exceed maximum representable values, resulting in unpredictable behavior.
The technical exploitation of this vulnerability leverages a combination of factors including the inherent integer overflow in the bdwgc garbage collector component, which is referenced as CVE-2016-9427. This interconnected nature of the vulnerability demonstrates how security flaws in supporting libraries can propagate to applications that depend on them. The integer overflow occurs during table rendering operations where memory allocation calculations become corrupted due to improper bounds checking. Attackers can craft HTML pages containing specially designed table structures that trigger the overflow condition, causing the application to allocate insufficient memory or attempt to allocate memory in invalid ranges.
From an operational perspective, this vulnerability presents significant risks to system stability and potentially allows for remote code execution. The denial of service condition manifests as out-of-memory errors that can crash the w3m browser application, rendering it unusable for legitimate users. However, the more concerning aspect involves the potential for arbitrary code execution, which could enable attackers to gain control over affected systems. The vulnerability's impact extends beyond simple application crashes since it affects a widely used text-based web browser that many users rely on for accessing web content, particularly in environments where graphical browsers are not available or appropriate.
The vulnerability aligns with CWE-190, which describes integer overflow and underflow conditions, and demonstrates how such flaws can be exploited in memory management contexts. From an attack framework perspective, this vulnerability would likely map to multiple ATT&CK techniques including TA0005 (Defense Evasion) through process injection and TA0002 (Execution) via arbitrary code execution capabilities. The exploitation requires only a web page with crafted HTML content, making it particularly dangerous in phishing campaigns or compromised websites. Organizations using w3m or its derivatives should consider this vulnerability as part of their broader security posture assessment, particularly in environments where text-based browsers are deployed for accessibility or security reasons.
Mitigation strategies should focus on immediate patch application to versions 0.5.3-31 or later, which contain fixes for both the integer overflow in renderTable and the underlying bdwgc issue. System administrators should also implement web content filtering and sandboxing measures to reduce exposure, particularly in environments where users may encounter untrusted web content. Regular security assessments should include evaluation of text-based browser implementations, as these applications often receive less security scrutiny than their graphical counterparts. Additionally, user education regarding the risks of visiting untrusted websites remains crucial, as social engineering aspects of exploitation may be leveraged to deliver malicious content to vulnerable systems.