CVE-2008-4690 in lynx
Summary
by MITRE
lynx 2.8.6dev.15 and earlier, when advanced mode is enabled and lynx is configured as a URL handler, allows remote attackers to execute arbitrary commands via a crafted lynxcgi: URL, a related issue to CVE-2005-2929. NOTE: this might only be a vulnerability in limited deployments that have defined a lynxcgi: handler.
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Analysis
by VulDB Data Team • 08/20/2019
The vulnerability described in CVE-2008-4690 represents a critical command injection flaw in the lynx web browser version 2.8.6dev.15 and earlier. This issue specifically manifests when the browser operates in advanced mode and has been configured to function as a URL handler for lynxcgi protocol. The vulnerability stems from insufficient input validation and sanitization within the URL parsing mechanism, creating an avenue for remote attackers to inject malicious commands through specially crafted lynxcgi: URLs. The flaw is particularly concerning because it leverages the browser's inherent capability to handle external URL protocols, which are typically designed for legitimate navigation purposes but can be exploited for unauthorized system access.
The technical nature of this vulnerability aligns with CWE-78, which identifies improper neutralization of special elements used in OS commands, and CWE-94, which covers improper control of generation of code. The attack vector involves a remote adversary constructing a malicious lynxcgi: URL that, when processed by the vulnerable lynx browser, triggers unintended command execution on the target system. This occurs because the browser fails to properly validate or escape the parameters embedded within the lynxcgi: URL scheme, allowing attackers to inject operating system commands that get executed with the privileges of the user running lynx. The vulnerability is classified as a code injection flaw that operates at the application layer, affecting the browser's protocol handler implementation.
The operational impact of this vulnerability extends beyond simple command execution, as it can potentially allow attackers to gain unauthorized access to the underlying system, escalate privileges, or perform other malicious activities. In environments where lynx is configured as a default browser or URL handler, particularly in restricted or automated systems, this vulnerability could enable complete system compromise. The limited deployment scope mentioned in the original description suggests that exploitation is most relevant in specific configurations where lynxcgi: handlers are explicitly defined, making the vulnerability less widespread but more dangerous in affected environments. This aligns with ATT&CK technique T1059, which covers command and scripting interpreter, and T1068, which addresses exploit for privilege escalation.
Mitigation strategies for CVE-2008-4690 should focus on immediate patching of the lynx browser to version 2.8.6dev.16 or later, which contains the necessary fixes for the command injection vulnerability. Organizations should also implement strict URL validation and sanitization policies for any applications that handle external protocol handlers, particularly those that execute system commands. Configuration management practices should include disabling unnecessary URL handlers and restricting the browser's ability to execute external commands through URL schemes. Additionally, network segmentation and access controls should limit the exposure of systems running vulnerable versions of lynx, while monitoring systems should be configured to detect suspicious URL patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of secure input handling in applications that process external protocol schemes and the need for comprehensive security testing of URL handling mechanisms.