CVE-2017-1000211 in Lynx
Summary
by MITRE
Lynx version 2.8.8 and older is vulnerable to a use after free in the HTML parser resulting in memory disclosure.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-1000211 affects Lynx version 2.8.8 and earlier, representing a critical use after free condition within the HTML parser component. This flaw occurs when the application processes malformed HTML content that triggers improper memory management during parsing operations. The vulnerability stems from the failure to properly validate memory references after objects have been freed, creating opportunities for memory disclosure attacks. The HTML parser in Lynx handles various document formats and markup structures, making it susceptible to exploitation through crafted input that manipulates the parser's internal state.
The technical implementation of this vulnerability involves memory management errors where allocated memory blocks are accessed after being freed, allowing attackers to potentially read sensitive data from memory locations that should no longer be accessible. This use after free condition typically arises when the parser encounters malformed HTML elements that cause the application to free memory associated with HTML node structures while still maintaining references to those locations. The memory disclosure aspect enables attackers to extract information from adjacent memory regions, potentially including stack contents, heap data, or other sensitive information that may be cached in memory. This type of vulnerability is classified under CWE-416 as Use After Free and falls within the broader category of memory safety issues that have been extensively documented in cybersecurity literature.
The operational impact of CVE-2017-1000211 extends beyond simple memory disclosure, as it represents a foundational security weakness that could enable more sophisticated attacks. Attackers could leverage this vulnerability to gain insights into the application's memory layout, potentially facilitating further exploitation techniques such as information leakage attacks or auxiliary attacks that depend on understanding memory organization. The vulnerability affects all versions of Lynx prior to 2.8.8, making it a widespread concern for users who have not updated their installations. Since Lynx is commonly used as a text-based web browser in server environments and terminal-based applications, the potential attack surface includes systems where users may encounter untrusted HTML content, particularly in automated contexts or when processing web feeds and other dynamic content sources.
Security mitigations for this vulnerability primarily involve immediate software updates to Lynx version 2.8.8 or later, which contain patches addressing the memory management issues in the HTML parser. Organizations should also implement input validation measures to filter potentially malicious HTML content before processing, though this approach provides only partial protection given the nature of the vulnerability. The fix typically involves ensuring proper memory deallocation and reference invalidation within the parser's handling of HTML structures, preventing access to freed memory blocks. From an operational security perspective, system administrators should conduct thorough vulnerability assessments to identify systems running vulnerable versions of Lynx and ensure prompt patch deployment. This vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as exploitation may involve crafting specific HTML content to trigger the memory corruption, and potentially T1068 for Exploitation for Privilege Escalation if the memory disclosure leads to further exploitation opportunities. The vulnerability demonstrates how seemingly minor memory management flaws in widely-used applications can create significant security risks, emphasizing the importance of robust memory safety practices in software development and the necessity of regular security updates.