CVE-2005-2929 in Lynx
Summary
by MITRE
Lynx 2.8.5, and other versions before 2.8.6dev.15, allows remote attackers to execute arbitrary commands via (1) lynxcgi:, (2) lynxexec, and (3) lynxprog links, which are not properly restricted in the default configuration in some environments.
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Analysis
by VulDB Data Team • 06/29/2025
The vulnerability identified as CVE-2005-2929 represents a critical command injection flaw in the Lynx web browser version 2.8.5 and earlier releases. This issue affects the default configuration of Lynx in certain environments where specific link protocols are not adequately restricted, creating a pathway for remote attackers to execute arbitrary commands on affected systems. The vulnerability specifically targets three distinct link protocols: lynxcgi, lynxexec, and lynxprog, which are designed to handle different types of external command execution scenarios within the browser environment. These protocols are intended to provide functionality for executing CGI scripts, external programs, and program execution respectively, but in the vulnerable versions they lack proper input validation and access control mechanisms.
The technical flaw stems from insufficient sanitization of user-supplied input within these protocol handlers, allowing attackers to inject malicious commands that are then executed with the privileges of the Lynx process. This represents a classic command injection vulnerability that can be exploited through crafted URLs containing these specific protocols. The vulnerability is particularly dangerous because it operates at the application level within the browser itself, bypassing traditional network-level security controls and potentially allowing attackers to execute commands directly on the host system. The default configuration in some environments fails to properly restrict these protocols, meaning that users who encounter specially crafted links could unknowingly trigger command execution without proper authorization checks. This flaw aligns with CWE-77 which specifically addresses command injection vulnerabilities where untrusted input is passed directly to system commands without proper sanitization.
The operational impact of this vulnerability extends beyond simple remote code execution, as it can enable attackers to gain unauthorized access to system resources, escalate privileges, and potentially establish persistent access to compromised systems. Attackers can leverage this vulnerability to execute system commands with the same privileges as the Lynx process, which typically runs with the permissions of the user who initiated the browser session. In environments where Lynx is used with elevated privileges or in automated contexts, the potential for damage increases significantly. The vulnerability affects not only individual users but also organizations that rely on Lynx for web browsing in restricted or automated environments. The exploitation requires minimal user interaction, as simply clicking on a maliciously crafted link containing one of the three vulnerable protocols can trigger the command injection. This makes the vulnerability particularly dangerous in phishing scenarios or when users browse untrusted web content.
Mitigation strategies for CVE-2005-2929 involve multiple layers of defensive measures to protect against exploitation. The primary recommendation is to upgrade to Lynx version 2.8.6dev.15 or later, which contains the necessary patches to address the command injection vulnerabilities in the affected protocols. Organizations should also implement strict configuration policies that disable or restrict the use of lynxcgi, lynxexec, and lynxprog protocols in environments where they are not strictly required for legitimate operations. Network-level controls such as firewall rules and proxy configurations can be implemented to block access to these specific protocol handlers. Additionally, users should be educated about the risks of clicking on untrusted links and the importance of verifying the source of web content before interacting with potentially malicious URLs. The vulnerability demonstrates the importance of proper input validation and privilege separation in application design, as it could have been prevented through better implementation of access controls and command sanitization. Organizations should also consider implementing web application firewalls or similar security controls that can detect and block attempts to exploit these specific protocol handlers. The incident underscores the critical need for regular security updates and proper configuration management in preventing exploitation of known vulnerabilities, as this flaw was present in widely deployed versions of the browser.