CVE-2002-0733 in thttpd
Summary
by MITRE
Cross-site scripting vulnerability in thttpd 2.20 and earlier allows remote attackers to execute arbitrary script via a URL to a nonexistent page, which causes thttpd to insert the script into a 404 error message.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability described in CVE-2002-0733 represents a classic cross-site scripting flaw in the thttpd web server software version 2.20 and earlier. This security weakness stems from the server's improper handling of malformed URL requests that result in 404 error responses. When a remote attacker submits a crafted URL pointing to a non-existent page, the thttpd server processes this request and incorporates the malicious script code directly into the generated 404 error message that gets sent back to the victim's browser. This behavior creates a persistent XSS vector that can be exploited to execute arbitrary JavaScript code within the context of any user who views the error page.
The technical nature of this vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in software applications. The flaw occurs because thttpd fails to properly sanitize or escape user input before including it in error responses, creating an environment where attacker-controlled data can be injected into the server's output. This particular implementation defect demonstrates poor input validation and output encoding practices that are fundamental to preventing XSS attacks. The vulnerability is particularly concerning because it leverages the server's standard error handling mechanism, making it difficult to detect and prevent through conventional security measures.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform various malicious activities including session hijacking, credential theft, and redirection to phishing sites. When users encounter the 404 error page containing the injected script, their browsers execute the malicious code within the context of the vulnerable web application, potentially compromising their session cookies and other sensitive information. This vulnerability affects all users who visit pages containing the malicious URL, making it a scalable attack vector that can be propagated through various means such as email links, social media posts, or compromised websites.
Mitigation strategies for this vulnerability should include immediate patching of the thttpd software to version 2.21 or later, where the XSS vulnerability has been addressed through proper input sanitization. Organizations should also implement comprehensive input validation at multiple layers of their web application architecture, including both server-side and client-side protections. Network administrators should consider implementing web application firewalls that can detect and block suspicious URL patterns, while security teams should conduct regular vulnerability assessments to identify similar flaws in other web server components. The remediation process should also include educating development teams about secure coding practices, particularly around input validation and output encoding, to prevent similar vulnerabilities from being introduced in future software releases. This vulnerability serves as a reminder of the critical importance of proper input sanitization in web applications, as outlined in the OWASP Top Ten security risks and the ATT&CK framework's web application attack patterns.