CVE-2021-47794: Zesle ZesleCP RCE Vulnerability

CVE-2021-47794 Overview

CVE-2021-47794 is an authenticated remote code execution vulnerability affecting ZesleCP 3.1.9, a web hosting control panel. The vulnerability allows attackers with valid authentication credentials to execute arbitrary commands on the underlying system through shell injection payloads embedded in FTP account creation requests. By exploiting the FTP account creation endpoint, attackers can inject malicious commands that establish reverse shell connections, gaining full control over the hosting server.

Critical Impact

Authenticated attackers can achieve complete system compromise by injecting shell commands through the FTP account creation functionality, potentially leading to data exfiltration, lateral movement, and persistent access to the hosting infrastructure.

Affected Products

• ZesleCP 3.1.9
• Zesle ZesleCP (all versions up to and including 3.1.9)

Discovery Timeline

• 2026-01-16 - CVE CVE-2021-47794 published to NVD
• 2026-01-21 - Last updated in NVD database

Technical Details for CVE-2021-47794

Vulnerability Analysis

This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The flaw exists in the FTP account creation functionality within ZesleCP's web interface.

When an authenticated user creates a new FTP account, the application fails to properly sanitize user-supplied input before passing it to system shell commands. This lack of input validation allows attackers to break out of the intended command context and inject arbitrary shell commands that execute with the privileges of the ZesleCP service account.

The network-accessible nature of this vulnerability, combined with the low attack complexity and absence of user interaction requirements, makes it particularly dangerous for organizations running ZesleCP in production environments. An attacker who has obtained valid credentials—through credential theft, brute force, or other means—can immediately leverage this flaw to establish a foothold on the server.

Root Cause

The root cause of CVE-2021-47794 is insufficient input sanitization in the FTP account creation handler. The application directly incorporates user-supplied parameters into shell commands without properly escaping or validating special characters. This allows attackers to terminate the intended command and append malicious instructions using shell metacharacters such as semicolons, pipes, or command substitution syntax.

Proper input validation should include whitelisting acceptable characters for FTP usernames, rejecting or escaping shell metacharacters, and ideally using parameterized system calls that avoid shell interpretation entirely.

Attack Vector

The attack is executed over the network against the ZesleCP web interface. An authenticated attacker submits a specially crafted FTP account creation request containing shell injection payloads in the username or password fields.

A typical exploitation scenario involves the attacker injecting a reverse shell command that connects back to an attacker-controlled listener. Once the connection is established, the attacker gains interactive shell access to the underlying system with the privileges of the web application service account.

The exploitation requires valid authentication credentials, meaning the attacker must first obtain access to a ZesleCP user account. However, once authenticated, the exploitation is straightforward and requires no additional user interaction or complex conditions. Technical details and proof-of-concept code are available in the Exploit-DB #50233 entry and the VulnCheck Advisory.

Detection Methods for CVE-2021-47794

Indicators of Compromise

• Unexpected outbound network connections from the ZesleCP server to external IP addresses, particularly on common reverse shell ports
• FTP account entries with usernames or passwords containing shell metacharacters (;, |, $(), backticks)
• Process spawning anomalies where the web server process spawns unexpected child processes such as /bin/bash, nc, or python
• Unusual system commands executed in the context of the ZesleCP web application user

Detection Strategies

• Monitor HTTP POST requests to the FTP account creation endpoint for payloads containing shell metacharacters or common command injection patterns
• Implement web application firewall (WAF) rules to detect and block command injection attempts in form parameters
• Enable comprehensive logging for the ZesleCP application and review logs for suspicious FTP account creation attempts
• Deploy endpoint detection and response (EDR) solutions capable of identifying process lineage anomalies

Monitoring Recommendations

• Configure network monitoring to alert on outbound connections from web servers to non-standard ports
• Establish baseline behavior for the ZesleCP service and alert on deviations such as new child processes or network connections
• Review FTP account database regularly for entries with suspicious naming patterns
• Implement file integrity monitoring on critical ZesleCP configuration and script files

How to Mitigate CVE-2021-47794

Immediate Actions Required

• Restrict access to the ZesleCP administrative interface to trusted IP addresses only
• Review all existing FTP accounts for suspicious entries that may indicate prior exploitation
• Implement strong authentication controls including multi-factor authentication where possible
• Consider temporarily disabling FTP account creation functionality until a patch is applied

Patch Information

Organizations using ZesleCP should check the ZesleCP Homepage for the latest version and security updates. Review release notes for any security fixes addressing command injection vulnerabilities. If no patch is available, consider migrating to an alternative hosting control panel with a stronger security track record.

For detailed technical information about this vulnerability, refer to the VulnCheck Advisory and Exploit-DB #50233.

Workarounds

• Implement network segmentation to isolate ZesleCP servers from critical infrastructure
• Deploy a reverse proxy with input validation rules to filter malicious requests before they reach ZesleCP
• Restrict shell access for the ZesleCP service account using tools like rbash or AppArmor profiles
• Monitor and rate-limit FTP account creation requests to slow potential exploitation attempts

# Example: Restrict access to ZesleCP admin interface using iptables
iptables -A INPUT -p tcp --dport 2087 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 2087 -j DROP