CVE-2016-9423 in w3m
Summary
by MITRE
An issue was discovered in the Tatsuya Kinoshita w3m fork before 0.5.3-31. Heap-based buffer overflow in w3m allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via a crafted HTML page.
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Analysis
by VulDB Data Team • 06/25/2019
The vulnerability identified as CVE-2016-9423 represents a critical heap-based buffer overflow flaw within the w3m web browser fork developed by Tatsuya Kinoshita. This security weakness exists in versions prior to 0.5.3-31 and demonstrates a classic memory corruption vulnerability that can be exploited through maliciously crafted HTML content. The w3m browser, known for its text-based interface and lightweight design, is widely used in environments where graphical web browsers are not available or practical, making this vulnerability particularly concerning for system administrators and security professionals who rely on such tools.
The technical implementation of this buffer overflow occurs within the memory management functions of the w3m application when processing HTML content. Attackers can construct specially formatted HTML pages that trigger the overflow condition in the heap memory allocation routines, causing unpredictable behavior in the application's execution flow. This type of vulnerability falls under the CWE-121 category of heap-based buffer overflow, where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The heap corruption typically manifests as application crashes during HTML parsing, but the vulnerability's potential for arbitrary code execution cannot be ruled out, especially when the overflow affects critical program structures or when combined with other exploitation techniques.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it represents a potential gateway for more sophisticated attacks within systems that depend on w3m for web content viewing. When exploited successfully, the buffer overflow could allow remote attackers to execute arbitrary code with the privileges of the w3m process, potentially leading to complete system compromise. The vulnerability affects environments where w3m is used as a default browser or integrated into automated systems, including embedded devices, server environments, and development workstations where text-based browsing is preferred. Organizations relying on w3m for automated content fetching or web-based applications may face significant security risks if this vulnerability remains unpatched.
Mitigation strategies for CVE-2016-9423 primarily focus on immediate version updates to w3m 0.5.3-31 or later releases that contain the necessary memory bounds checking fixes. System administrators should prioritize patching affected installations across all environments where w3m is deployed, particularly in server and embedded systems where the browser may be used in automated contexts. Additional defensive measures include implementing web content filtering mechanisms to prevent access to untrusted HTML content, deploying network-based intrusion detection systems that can identify exploitation attempts, and conducting regular security assessments of systems that utilize w3m. The vulnerability aligns with ATT&CK technique T1203, which involves the use of malicious content to gain execution privileges, and demonstrates the importance of maintaining up-to-date software versions as a fundamental security control. Organizations should also consider implementing sandboxing techniques for web browsing activities to limit the potential impact of successful exploitation attempts.