CVE-2016-9435 in w3m
Summary
by MITRE
The HTMLtagproc1 function in file.c in w3m before 0.5.3+git20161009 does not properly initialize values, which allows remote attackers to crash the application via a crafted html file, related to <dd> tags.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2016-9435 represents a critical memory safety issue within the w3m web browser's HTML processing engine. This flaw exists in the HTMLtagproc1 function located in the file.c component of w3m versions prior to 0.5.3+git20161009, where improper initialization of variables creates a predictable crash condition that can be exploited by remote attackers. The vulnerability specifically targets the processing of <dd> HTML tags, which are used to define description terms in definition lists, making it particularly concerning for web content that utilizes structured markup. The improper initialization allows attackers to craft malicious HTML files that trigger undefined behavior when the w3m browser attempts to parse these tags, leading to application instability and potential system compromise.
The technical nature of this vulnerability aligns with CWE-457, which describes the use of uninitialized variables in software systems, and represents a classic example of a memory safety issue that can lead to denial of service or potentially more severe exploitation scenarios. When the HTMLtagproc1 function processes a crafted <dd> tag, the uninitialized memory values can cause the application to access invalid memory locations or execute malformed code paths, resulting in segmentation faults or other crash conditions. This vulnerability falls under the ATT&CK technique T1203, which involves exploiting software vulnerabilities to cause system instability or denial of service, and demonstrates how seemingly minor initialization flaws can create significant security risks in web browsing applications.
The operational impact of CVE-2016-9435 extends beyond simple application crashes, as it can be leveraged to disrupt web browsing services or potentially provide a foothold for more sophisticated attacks. Remote attackers can craft HTML content that, when viewed through vulnerable w3m installations, will trigger the crash condition, making this a particularly dangerous vulnerability for web applications or services that rely on w3m for HTML rendering. The vulnerability affects systems where w3m is used as a text-based browser or integrated into larger applications, and the exploit requires minimal sophistication to be effective, making it a significant concern for organizations that may be using vulnerable versions of this software.
Mitigation strategies for CVE-2016-9435 primarily involve upgrading to w3m version 0.5.3 or later, which contains the necessary patches to properly initialize variables in the HTMLtagproc1 function. System administrators should also implement network-based protections such as web application firewalls that can detect and block malicious HTML content before it reaches vulnerable systems, and consider implementing content filtering measures that sanitize HTML input. Additionally, organizations should conduct vulnerability assessments to identify all systems running vulnerable versions of w3m and ensure that proper patch management procedures are in place to prevent similar issues from occurring in other software components. The remediation process should also include monitoring for exploitation attempts and implementing proper logging to detect when malicious HTML content is being processed by affected systems.