CVE-2016-9627 in w3m
Summary
by MITRE
An issue was discovered in the Tatsuya Kinoshita w3m fork before 0.5.3-33. w3m allows remote attackers to cause a denial of service (heap buffer overflow and crash) via a crafted HTML page.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-9627 represents a critical heap buffer overflow flaw within the w3m web browser fork developed by Tatsuya Kinoshita. This issue affects versions prior to 0.5.3-33 and demonstrates how seemingly benign web content can be weaponized to disrupt system operations. The vulnerability resides in the HTML parsing mechanisms of the w3m browser, specifically within its handling of malformed or crafted HTML elements that trigger memory corruption during rendering processes.
The technical implementation of this vulnerability involves improper bounds checking during HTML document parsing, particularly when processing specific combinations of HTML tags and attributes. When a maliciously crafted HTML page is loaded, the w3m browser attempts to allocate memory for buffer operations without adequate validation of input data lengths. This leads to a heap-based buffer overflow condition where data written beyond allocated memory boundaries corrupts adjacent heap memory structures. The overflow occurs in the memory management subsystem responsible for handling HTML element rendering, specifically affecting the browser's ability to properly manage dynamic memory allocation for text and element storage.
The operational impact of this vulnerability extends beyond simple denial of service, as it provides attackers with a mechanism to potentially execute arbitrary code or cause system instability. Remote attackers can leverage this flaw by hosting malicious HTML content on web servers, which when accessed through the vulnerable w3m browser instance triggers the buffer overflow condition. The crash occurs during normal browsing operations when the browser attempts to render the crafted HTML content, making this a particularly dangerous vulnerability for users who may inadvertently encounter malicious web pages. This vulnerability affects both desktop and server environments where w3m is used for web content rendering or automated browsing tasks.
Security practitioners should prioritize patching affected systems to mitigate this vulnerability, as the heap buffer overflow can potentially be exploited for more sophisticated attacks beyond simple denial of service. The vulnerability aligns with CWE-121, heap-based buffer overflow, and represents a classic example of insufficient input validation in memory management operations. Mitigation strategies should include immediate deployment of w3m version 0.5.3-33 or later, which incorporates proper bounds checking and memory allocation validation. Organizations should also consider implementing web filtering solutions to block access to known malicious content and establish monitoring procedures to detect potential exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1203, "Exploitation for Client Execution, as it enables remote code execution through web browser exploitation techniques.
This vulnerability demonstrates the critical importance of proper memory management in browser implementations and highlights the risks associated with legacy code bases that may not have received adequate security updates. The flaw serves as a reminder of the ongoing need for comprehensive security testing, particularly in components that handle untrusted input data such as web content parsing. System administrators should conduct thorough inventory assessments to identify all affected w3m installations and ensure that security patches are deployed across all environments where this browser fork is utilized for web browsing operations.