CVE-2025-41357 Overview
A reflected Cross-Site Scripting (XSS) vulnerability has been identified in Anon Proxy Server v0.104. This security flaw allows attackers to execute arbitrary JavaScript code in a victim's browser by tricking them into clicking a malicious URL. The vulnerability specifically affects the host parameter in the /diagdns.php endpoint, where user-supplied input is reflected back to the browser without proper sanitization.
This vulnerability can be exploited to steal sensitive user data, such as session cookies, or to perform actions on behalf of the user within the context of the vulnerable application.
Critical Impact
Attackers can execute malicious JavaScript in victim browsers to steal session cookies, hijack user sessions, or perform unauthorized actions on behalf of authenticated users.
Affected Products
- Anon Proxy Server v0.104
Discovery Timeline
- 2026-03-31 - CVE-2025-41357 published to NVD
- 2026-04-01 - Last updated in NVD database
Technical Details for CVE-2025-41357
Vulnerability Analysis
This reflected XSS vulnerability (CWE-79) occurs in the diagnostic DNS functionality of Anon Proxy Server. When a user accesses the /diagdns.php endpoint, the application accepts a host parameter that is intended for DNS diagnostic operations. However, the application fails to properly sanitize or encode this parameter before reflecting it back in the HTTP response.
The attack requires user interaction—specifically, the victim must click a crafted malicious link. Once clicked, the attacker-controlled JavaScript executes within the security context of the vulnerable application, allowing access to cookies, session tokens, and the ability to make authenticated requests on behalf of the victim.
Root Cause
The vulnerability stems from improper input validation and output encoding in the /diagdns.php endpoint. The host parameter is directly reflected in the page output without being sanitized for HTML special characters or JavaScript context. This allows attackers to inject script tags or event handlers that execute when the page renders in the victim's browser.
Attack Vector
An attacker crafts a malicious URL containing JavaScript payload in the host parameter of the /diagdns.php endpoint. The attacker then distributes this URL through phishing emails, social engineering, or by embedding it in web pages. When a victim clicks the link, the malicious script executes in their browser with full access to the user's session within the Anon Proxy Server application.
The attack is network-based and requires the victim to actively click the malicious link. Once executed, the attacker can steal session cookies, capture keystrokes, redirect users to phishing sites, or perform actions as the authenticated user.
Detection Methods for CVE-2025-41357
Indicators of Compromise
- Unusual requests to /diagdns.php containing script tags or JavaScript event handlers in the host parameter
- Web server logs showing encoded characters such as %3Cscript%3E or %22onmouseover%3D in query strings
- Users reporting unexpected behavior after clicking links pointing to the proxy server's diagnostic endpoints
Detection Strategies
- Implement web application firewall (WAF) rules to detect and block XSS patterns in the host parameter
- Monitor web server access logs for requests to /diagdns.php containing suspicious payloads
- Deploy browser-based XSS protection headers and Content Security Policy (CSP) to limit script execution
- Use intrusion detection systems to flag HTTP requests with common XSS payload signatures
Monitoring Recommendations
- Enable detailed logging for the /diagdns.php endpoint and review logs for anomalous parameter values
- Configure alerts for requests containing HTML or JavaScript syntax in URL parameters
- Monitor for unusual patterns of user session activity that may indicate session hijacking
How to Mitigate CVE-2025-41357
Immediate Actions Required
- Restrict access to the /diagdns.php endpoint to authorized administrators only
- Implement input validation to reject or sanitize the host parameter before processing
- Deploy Content Security Policy headers to prevent inline script execution
- Consider disabling the diagnostic DNS functionality if not operationally required
Patch Information
No official patch information is currently available from the vendor. Organizations should monitor the INCIBE Security Notice on XSS for updates and remediation guidance.
Workarounds
- Block or restrict access to /diagdns.php at the network or web server level until a patch is available
- Implement a web application firewall rule to filter XSS patterns in requests to the affected endpoint
- Educate users about the risks of clicking untrusted links, especially those pointing to administrative interfaces
- Consider deploying a reverse proxy with input sanitization capabilities in front of the vulnerable application
# Example: Apache configuration to restrict access to vulnerable endpoint
<Location /diagdns.php>
Order deny,allow
Deny from all
Allow from 192.168.1.0/24
</Location>
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
