CVE-2026-27146: GetSimple CMS CSRF Vulnerability

CVE-2026-27146 Overview

CVE-2026-27146 is a Cross-Site Request Forgery (CSRF) vulnerability affecting all versions of GetSimple CMS. The content management system fails to implement CSRF protection on its administrative file upload endpoint, allowing attackers to craft malicious web pages that silently trigger file upload requests from authenticated victims' browsers. The request is accepted without requiring a CSRF token or origin validation, enabling attackers to upload arbitrary files to the application without the victim's knowledge or consent.

Critical Impact

Attackers can upload arbitrary files including malicious PHP scripts to GetSimple CMS installations, potentially leading to remote code execution and complete server compromise when an authenticated administrator visits a malicious webpage.

Affected Products

• GetSimple CMS Community Edition (all versions)
• getsimple-ce getsimple_cms

Discovery Timeline

• 2026-02-21 - CVE-2026-27146 published to NVD
• 2026-02-24 - Last updated in NVD database

Technical Details for CVE-2026-27146

Vulnerability Analysis

This vulnerability exists because GetSimple CMS does not implement any form of CSRF protection on its administrative file upload functionality. When an administrator is logged into the CMS and visits an attacker-controlled webpage, the attacker can craft hidden HTML forms or JavaScript code that automatically submits file upload requests to the CMS. Since the CMS does not validate CSRF tokens or check the request origin, these requests are processed as legitimate administrative actions.

The impact of this vulnerability is severe because successful exploitation allows arbitrary file uploads. An attacker could upload malicious PHP files, backdoors, or web shells that would then be accessible and executable on the target server. This transforms a CSRF vulnerability into a potential remote code execution scenario.

Root Cause

The root cause is the complete absence of CSRF protection mechanisms on the administrative file upload endpoint. Proper implementation would require:

1. Generation of unique CSRF tokens bound to user sessions
2. Validation of these tokens on all state-changing requests
3. Origin header validation to ensure requests originate from the same site
4. SameSite cookie attributes to prevent cross-origin request inclusion

GetSimple CMS implements none of these protections, leaving the file upload functionality exposed to cross-site request attacks.

Attack Vector

The attack requires the victim to be authenticated to GetSimple CMS (typically as an administrator) and to visit an attacker-controlled webpage. The attack is network-based and requires user interaction (visiting the malicious page), but no privileges are required by the attacker themselves.

The attacker hosts a webpage containing a hidden form that targets the GetSimple CMS file upload endpoint. When the victim visits this page, JavaScript automatically submits the form, uploading the attacker's chosen file to the CMS installation. The victim has no indication that this action has occurred.

A typical attack scenario involves social engineering to lure administrators to visit attacker-controlled pages, email phishing campaigns with embedded links, or compromised legitimate websites that include the attack code.

Detection Methods for CVE-2026-27146

Indicators of Compromise

• Unexpected files appearing in the GetSimple CMS uploads directory or theme folders
• New PHP files or executable scripts in the CMS installation that were not intentionally added
• Web server access logs showing file upload requests originating from external referrers
• Unusual administrator session activity correlating with visits to external sites

Detection Strategies

• Monitor file system changes within the GetSimple CMS installation directory for newly created files
• Implement web application firewall (WAF) rules to detect and block cross-origin file upload attempts
• Review web server access logs for POST requests to upload endpoints with suspicious referer headers
• Deploy file integrity monitoring to alert on unauthorized file additions

Monitoring Recommendations

• Enable detailed logging of all administrative actions within GetSimple CMS
• Configure intrusion detection systems to monitor for web shell signatures in uploaded content
• Establish baseline file inventories and alert on deviations
• Implement network traffic analysis to identify data exfiltration following potential compromise

How to Mitigate CVE-2026-27146

Immediate Actions Required

• Restrict administrative access to GetSimple CMS to trusted networks only using firewall rules or VPN requirements
• Implement additional authentication layers such as HTTP Basic Auth or IP-based restrictions on the admin directory
• Educate administrators about the risks of visiting untrusted websites while logged into the CMS
• Consider deploying a reverse proxy with CSRF protection capabilities in front of the CMS

Patch Information

This vulnerability does not have a fix at the time of publication. GetSimple CMS Community Edition has not released a security patch addressing this CSRF issue. Organizations should implement compensating controls until an official fix becomes available.

For the latest information on this vulnerability, refer to the GitHub Security Advisory GHSA-26rv-8wpp-q84r.

Workarounds

• Configure SameSite cookie attributes at the web server level to prevent cookies from being sent with cross-origin requests
• Deploy a web application firewall (WAF) with CSRF detection capabilities
• Restrict access to the CMS admin panel by IP address or VPN requirement
• Use browser extensions that block cross-origin requests when logged into administrative interfaces
• Consider migrating to an alternative CMS with proper CSRF protection until a patch is available

# Apache .htaccess example to restrict admin access by IP
<Directory "/var/www/html/getsimple/admin">
    # Allow only specific IP addresses
    Require ip 192.168.1.0/24
    Require ip 10.0.0.100
    # Deny all other IPs
    Require all denied
</Directory>

# Nginx configuration to restrict admin access
location /admin {
    allow 192.168.1.0/24;
    allow 10.0.0.100;
    deny all;
}