CVE-2025-58801

Executive Summary

CVE-2025-58801 is a Cross-Site Request Forgery (CSRF) vulnerability affecting the KCS Responder application, specifically versions up to and including 4.3.8. This vulnerability allows an attacker to perform unauthorized actions on behalf of an authenticated user, such as modifying settings or executing privileged operations, without the user's consent. The vulnerability is classified under CWE-352 and has a CVSS score of 5.4 (Medium). As of the latest intelligence, no official patch is available, and no public proof-of-concept (PoC) or exploit code has been released. The EPSS score is 0.0%, indicating a low probability of exploitation in the wild at this time.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a standalone web application (KCS Responder) and does not involve package manager supply chain risks.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
• Base Score: 5.4 (Medium)
• Attack Vector: Network (AV:N) – The attack can be launched remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – The attacker does not need prior authentication.
• User Interaction: Required (UI:R) – The victim must click a link or visit a malicious page.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: Low (C:L) – Limited data exposure possible.
• Integrity Impact: Low (I:L) – Limited modification of data possible.
• Availability Impact: None (A:N) – No denial of service.

Threat Level: Medium. The requirement for user interaction reduces the immediate risk, but the lack of a patch and the potential for chaining with other vulnerabilities (e.g., XSS) could elevate the severity.

Deep Dive & Mechanics

The vulnerability resides in the KCS Responder application, which is likely a web-based incident response or ticketing system. The CSRF flaw allows an attacker to craft a malicious HTTP request (e.g., via a hidden form or image tag) that, when executed by an authenticated user, performs state-changing operations on the Responder instance. Common attack vectors include:

• Changing user passwords or permissions.
• Modifying system configurations.
• Deleting or altering tickets/data.
• Executing administrative actions.

The root cause is the absence of anti-CSRF tokens (e.g., nonces) in sensitive forms or API endpoints. The application does not validate the origin or referrer of requests, making it susceptible to cross-origin attacks.

Attack Flow:

1. Attacker identifies a state-changing endpoint (e.g., /admin/update_settings).
2. Attacker crafts a malicious HTML page with a form that auto-submits to that endpoint.
3. Victim (authenticated to Responder) visits the attacker's page.
4. The form submits the request with the victim's session cookies.
5. The server processes the request, believing it is legitimate.

Vulnerable vs. Patched Code

Since no patch is available, a comparison cannot be made. However, a typical fix would involve:

Vulnerable Code (Example):

// No CSRF token check
if ($_POST['action'] == 'update_settings') {
    update_option('responder_setting', $_POST['value']);
}

Patched Code (Expected):

// CSRF token validation
if (!wp_verify_nonce($_POST['_wpnonce'], 'responder_update_settings')) {
    die('CSRF validation failed.');
}
if ($_POST['action'] == 'update_settings') {
    update_option('responder_setting', $_POST['value']);
}

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A running instance of KCS Responder <= 4.3.8.
• An authenticated user session (victim).

Exploitation Steps:

1. Identify a CSRF-vulnerable endpoint (e.g., /wp-admin/admin-ajax.php?action=responder_delete_ticket).
2. Create a malicious HTML file (csrf_exploit.html):

<html>
<body>
<form action="http://target.com/wp-admin/admin-ajax.php" method="POST">
    <input type="hidden" name="action" value="responder_delete_ticket">
    <input type="hidden" name="ticket_id" value="123">
    <input type="submit" value="Click me">
</form>
<script>document.forms[0].submit();</script>
</body>
</html>

3. Host the file on an attacker-controlled server.
4. Send the link to the victim (e.g., via phishing email).
5. When the victim clicks, the request is sent with their session cookies.

Note: No public exploit code is available; this is a generic CSRF example.

Blue Team (Defense & Detection)

Detection:

• Monitor for unexpected POST requests to sensitive endpoints without a valid Referer header.
• Use web application firewalls (WAF) to block requests with missing or mismatched Origin headers.
• Implement CSRF tokens in all state-changing forms.

Honeypot:

• Deploy a decoy endpoint that logs all requests without CSRF tokens.

Indicators of Compromise (IOCs)

• Network:
  • Unusual POST requests to /wp-admin/admin-ajax.php or /admin/ endpoints with parameters like action=responder_*.
  • Referer headers pointing to external domains.
• Logs:
  • Multiple failed CSRF token validation attempts (if logging is enabled).
  • Unexpected changes to user roles or settings.
• File System:
  • No specific file IOCs; the attack is network-based.

Detection Engineering

YARA Rule

rule detect_csrf_responder {
    meta:
        description = "Detects CSRF attempts against KCS Responder"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-58801"
    strings:
        $action = "responder_" ascii wide nocase
        $csrf_bypass = "action=" ascii wide nocase
    condition:
        $action and $csrf_bypass
}

Sigma Rule

title: CSRF Attempt Against KCS Responder
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential CSRF attacks targeting KCS Responder
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'action=responder_'
    condition: selection
falsepositives:
    - Legitimate admin actions
level: medium

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (
    msg:"CVE-2025-58801 CSRF Attempt Against KCS Responder";
    flow:to_server,established;
    http.method; content:"POST";
    http.uri; content:"action=responder_";
    http.referer; content:!"|2f|"; nocase;
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable vulnerable endpoints if possible, or restrict access via IP whitelisting.
2. Implement CSRF tokens in all forms and AJAX requests (e.g., using WordPress nonces if applicable).
3. Validate HTTP Referer/Origin headers on the server side.
4. Use SameSite cookies (set to Lax or Strict) to prevent cross-origin requests.

Long-Term Fix:

• Apply the official patch once released by KCS.
• Upgrade to a patched version (if available).
• Conduct a security audit of all state-changing operations.

Workarounds:

• Deploy a WAF rule to block requests without a valid Referer.
• Use browser extensions like NoScript or uMatrix to limit cross-site requests.

Valters IT
Securing Digital Frontiers