CVE-2021-47937: e107 CMS 2.3.0 RCE Vulnerability

CVE-2021-47937 Overview

CVE-2021-47937 is an authenticated remote code execution vulnerability in e107 CMS version 2.3.0. The flaw resides in the theme upload functionality exposed through the theme.php endpoint. Authenticated users with theme installation permissions can upload a crafted theme package containing a malicious PHP payload. The package deploys a web shell to the e107_themes directory. Attackers then invoke payload.php to execute arbitrary operating system commands under the web server account. The vulnerability is classified under CWE-434: Unrestricted Upload of File with Dangerous Type.

Critical Impact
Authenticated attackers with theme management privileges can achieve full remote code execution on the underlying web server, leading to complete compromise of the CMS and hosting environment.

Affected Products

e107 CMS version 2.3.0
e107 installations exposing the theme.php administrative endpoint
Web servers hosting e107 with default e107_themes directory permissions

Discovery Timeline

2026-05-10 - CVE-2021-47937 published to NVD
2026-05-12 - Last updated in NVD database

Technical Details for CVE-2021-47937

Vulnerability Analysis

The vulnerability stems from insufficient validation of uploaded theme archives in e107 CMS 2.3.0. The CMS allows administrators to install themes by uploading archive packages through the theme.php administrative interface. The application extracts the contents of these archives into the e107_themes directory without validating file types or sanitizing PHP scripts contained within the package.

An attacker authenticated with theme installation privileges can craft a theme package that bundles a PHP web shell, typically named payload.php. Once uploaded, the file is written to a web-accessible location under e107_themes. The attacker then issues HTTP requests directly to the deployed shell, passing arbitrary commands through request parameters. Commands execute with the privileges of the PHP process, providing a foothold for lateral movement, data exfiltration, or persistence.

This class of weakness aligns with CWE-434, where the application accepts file uploads of dangerous types without restriction.

Root Cause

The root cause is the absence of server-side validation on files contained within theme archives. The installer trusts the archive structure and extracts PHP files into a directory served by the web server. Filename extensions, MIME types, and file content are not inspected against an allow-list of safe theme assets.

Attack Vector

Exploitation requires network access to the e107 administrative interface and valid credentials with theme management permissions. The attacker uploads a malicious theme package through theme.php, then sends an HTTP request to the dropped payload.php file in e107_themes with command parameters. Technical details and a working proof-of-concept are documented in the Exploit-DB entry #50315 and the VulnCheck Advisory for e107 CMS.

Detection Methods for CVE-2021-47937

Indicators of Compromise

Unexpected PHP files such as payload.php or similarly named scripts inside the e107_themes directory
HTTP POST requests to theme.php originating from non-administrative IP addresses
Outbound network connections initiated by the PHP worker process to unknown hosts
New or modified theme directories created outside of scheduled administrative changes

Detection Strategies

Monitor the e107_themes directory for newly created .php files outside legitimate theme assets
Inspect web server access logs for sequences combining theme.php uploads followed by direct requests to recently created PHP files
Correlate child processes spawned by the PHP-FPM or web server process, such as sh, bash, or cmd.exe, with preceding theme upload activity

Monitoring Recommendations

Enable file integrity monitoring on the entire e107_themes tree and the e107 administrative scripts
Forward web access logs and process telemetry to a centralized analytics platform for correlation
Alert on administrative authentication events followed within minutes by file system writes under web-served directories

How to Mitigate CVE-2021-47937

Immediate Actions Required

Restrict access to the e107 administrative interface using network segmentation, VPN, or IP allow-listing
Audit all accounts with theme installation privileges and revoke unnecessary administrative permissions
Review the e107_themes directory for unauthorized PHP files and remove any web shells
Rotate administrative credentials and session tokens for all e107 users

Patch Information

No official vendor patch reference is listed in the NVD record at the time of publication. Administrators should consult the e107 Official Website and the e107 Downloads Page for the latest stable release that addresses theme upload validation. The VulnCheck Advisory for e107 CMS tracks remediation status.

Workarounds

Disable the theme upload feature for all non-essential administrators until a patched release is deployed
Configure the web server to deny PHP execution within the e107_themes directory using server-level handler restrictions
Apply a Web Application Firewall rule to block multipart uploads to theme.php from untrusted sources
Run the PHP process under a least-privilege account that cannot write outside designated upload paths

bash

# Apache configuration example: deny PHP execution inside theme uploads
<Directory "/var/www/e107/e107_themes">
    <FilesMatch "\.(php|phtml|phar)$">
        Require all denied
    </FilesMatch>
</Directory>