CVE-2025-41356 Overview
A Reflected Cross-Site Scripting (XSS) vulnerability has been identified in Anon Proxy Server v0.104. This vulnerability allows an attacker to execute arbitrary JavaScript code in a victim's browser by crafting and sending a malicious URL. The flaw specifically affects the host parameter in the /diagconnect.php endpoint, enabling attackers to inject malicious scripts that execute within the context of the vulnerable application.
Successful exploitation of this vulnerability can lead to theft of sensitive user data, including session cookies, enabling session hijacking. Attackers may also perform unauthorized actions on behalf of authenticated users, potentially compromising the integrity of user accounts and data managed through the proxy server.
Critical Impact
Attackers can steal session cookies and execute actions on behalf of users by exploiting the unvalidated host parameter in /diagconnect.php.
Affected Products
- Anon Proxy Server v0.104
Discovery Timeline
- 2026-03-31 - CVE-2025-41356 published to NVD
- 2026-04-01 - Last updated in NVD database
Technical Details for CVE-2025-41356
Vulnerability Analysis
This Reflected XSS vulnerability occurs when user-supplied input via the host parameter is improperly handled by the /diagconnect.php endpoint. When a victim clicks on a maliciously crafted URL containing JavaScript payload in the host parameter, the server reflects this input back to the browser without adequate sanitization or encoding. The browser then interprets and executes the injected script within the security context of the vulnerable web application.
The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), which covers scenarios where user-controllable input is included in output without proper validation, allowing script injection attacks.
Root Cause
The root cause of this vulnerability lies in insufficient input validation and output encoding in the /diagconnect.php endpoint. The host parameter accepts user input that is reflected directly in the HTTP response without proper sanitization or HTML entity encoding. This allows special characters and JavaScript code to be interpreted by the browser as executable content rather than plain text.
Attack Vector
The attack is network-based and requires user interaction to succeed. An attacker must craft a malicious URL containing a JavaScript payload in the host parameter and convince a victim to click on it. Common delivery mechanisms include phishing emails, social media links, or embedding the malicious link in a compromised website.
When the victim clicks the link, their browser sends a request to the vulnerable Anon Proxy Server, which reflects the malicious payload back in the response. The victim's browser then executes the JavaScript code, which can access cookies, session tokens, or other sensitive information available in the browser context for the affected domain.
The exploitation mechanism involves injecting script tags or JavaScript event handlers through the host parameter. For example, an attacker could craft a URL that includes script content that executes when the page renders, exfiltrating session cookies to an attacker-controlled server. For detailed technical information, refer to the Incibe CERT Security Notice.
Detection Methods for CVE-2025-41356
Indicators of Compromise
- HTTP requests to /diagconnect.php containing suspicious characters in the host parameter such as <script>, javascript:, or encoded variants
- Outbound connections from user browsers to unknown external domains immediately after accessing proxy server pages
- Unusual URL patterns in web server logs containing Base64-encoded payloads or URL-encoded script tags in the host parameter
Detection Strategies
- Deploy web application firewall (WAF) rules to detect and block XSS payloads targeting the /diagconnect.php endpoint
- Implement browser security headers including Content-Security-Policy (CSP) to restrict script execution
- Monitor web server access logs for requests containing XSS signature patterns in the host parameter
Monitoring Recommendations
- Enable detailed logging for the /diagconnect.php endpoint to capture full request parameters
- Configure alerting for HTTP requests containing JavaScript-related keywords or HTML tags in URL parameters
- Review network traffic for unusual data exfiltration patterns following proxy server access
How to Mitigate CVE-2025-41356
Immediate Actions Required
- Restrict access to /diagconnect.php to authorized administrators only until a patch is available
- Implement WAF rules to filter malicious input targeting the host parameter
- Apply Content-Security-Policy headers to prevent inline script execution on the application
Patch Information
No official patch information is currently available from the vendor. Organizations should monitor the Incibe CERT Security Notice for updates regarding security fixes. In the interim, apply the recommended workarounds and consider restricting access to the vulnerable endpoint.
Workarounds
- Disable or restrict access to the /diagconnect.php endpoint if it is not required for operations
- Implement input validation on the server-side to sanitize the host parameter before processing
- Configure web application firewall rules to block requests containing script tags or JavaScript keywords in URL parameters
- Enable HTTPOnly and Secure flags on session cookies to reduce the impact of potential cookie theft
# Apache configuration to restrict access to vulnerable endpoint
<Location /diagconnect.php>
Require ip 10.0.0.0/8
Require ip 192.168.0.0/16
</Location>
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
