CVE-2021-47778: GetSimple CMS My SMTP Contact RCE Flaw

CVE-2021-47778 Overview

CVE-2021-47778 is a PHP code injection vulnerability affecting GetSimple CMS My SMTP Contact Plugin version 1.1.2. This vulnerability allows an authenticated administrator to inject arbitrary PHP code through plugin configuration parameters, leading to remote code execution on the server. The vulnerability is classified as CWE-94 (Improper Control of Generation of Code), representing a serious security flaw in the plugin's input validation mechanisms.

Critical Impact

Authenticated administrators can achieve full remote code execution on the web server by injecting malicious PHP code through the SMTP plugin configuration interface, potentially compromising the entire web application and underlying server infrastructure.

Affected Products

• GetSimple CMS My SMTP Contact Plugin version 1.1.2
• GetSimple CMS installations with the vulnerable plugin enabled
• Web servers hosting affected GetSimple CMS deployments

Discovery Timeline

• 2026-01-21 - CVE CVE-2021-47778 published to NVD
• 2026-01-21 - Last updated in NVD database

Technical Details for CVE-2021-47778

Vulnerability Analysis

The vulnerability resides in the My SMTP Contact Plugin's configuration handling mechanism. When an administrator configures SMTP settings through the plugin interface, the input parameters are not properly sanitized before being processed. This allows malicious PHP code to be injected into configuration fields, which is subsequently executed by the server when the configuration is loaded or processed.

The attack requires administrative authentication, which limits the initial attack surface. However, this constraint can be bypassed through chained attacks such as Cross-Site Request Forgery (CSRF) or Cross-Site Scripting (XSS) that target administrator sessions. Publicly available proof-of-concept exploits demonstrate this attack chain, combining CSRF with XSS to ultimately achieve remote code execution.

Root Cause

The root cause of this vulnerability is improper input validation and insufficient sanitization of user-supplied data within the plugin configuration parameters. The plugin fails to implement proper encoding, escaping, or validation of configuration values before they are stored and subsequently processed as PHP code. This allows arbitrary PHP code embedded within configuration strings to be executed in the context of the web server.

Attack Vector

The attack is network-based and requires an attacker to either have authenticated administrator access or chain the vulnerability with other attack vectors (such as CSRF or XSS) to execute malicious actions on behalf of an authenticated administrator. The attacker injects PHP code into the plugin's configuration fields, such as SMTP server settings or email template parameters. When the plugin processes these configuration values, the injected code is executed on the server, providing the attacker with full code execution capabilities.

The vulnerability can be exploited to achieve persistent backdoor access, data exfiltration, lateral movement within the network, or complete server compromise depending on the server's configuration and the injected payload.

Detection Methods for CVE-2021-47778

Indicators of Compromise

• Unexpected modifications to GetSimple CMS plugin configuration files, particularly my_smtp_contact related settings
• Unusual PHP files or web shells appearing in the GetSimple CMS installation directory
• Suspicious outbound network connections from the web server to unknown destinations
• Abnormal process execution initiated by the web server process (e.g., /bin/sh, cmd.exe, or other shell processes)
• Log entries showing configuration changes to SMTP plugin settings from suspicious IP addresses or at unusual times

Detection Strategies

• Monitor GetSimple CMS administrative access logs for suspicious configuration modification attempts
• Implement file integrity monitoring (FIM) on CMS installation directories to detect unauthorized changes
• Deploy web application firewalls (WAF) with rules to detect PHP code injection patterns in POST requests
• Review server access logs for patterns consistent with known exploit chains (CSRF to XSS to RCE)

Monitoring Recommendations

• Enable verbose logging for GetSimple CMS administrative actions and regularly review logs
• Configure SIEM alerts for anomalous web server behavior including unusual child process spawning
• Implement network monitoring for command-and-control (C2) communication patterns from web server hosts
• Set up automated scanning for known web shells and backdoor indicators in web-accessible directories

How to Mitigate CVE-2021-47778

Immediate Actions Required

• Audit administrator accounts and remove unnecessary access privileges to minimize attack surface
• Disable or uninstall the My SMTP Contact Plugin version 1.1.2 until a patched version is available
• Review server logs and configuration files for signs of previous exploitation
• Implement network segmentation to limit the impact of potential server compromise
• Enable Web Application Firewall (WAF) rules to block suspicious PHP code patterns in requests

Patch Information

As of the published date, users should check for updates to the My SMTP Contact Plugin from the official GetSimple CMS plugin repository. Additional information can be found through the GetSimple CMS Homepage and the GitHub GetSimpleCMS Repository. For detailed vulnerability information, refer to the VulnCheck Advisory for GetSimple CMS and Exploit-DB #49774.

Workarounds

• Disable the My SMTP Contact Plugin entirely if SMTP functionality is not critical to operations
• Implement strict Content Security Policy (CSP) headers to mitigate chained XSS attacks
• Enable CSRF protection tokens for all administrative actions in GetSimple CMS
• Restrict administrative access to trusted IP addresses only using server-level access controls
• Consider migrating to an alternative CMS or contact form solution until a secure plugin version is released

# Example: Restrict administrative access by IP using .htaccess
# Place in GetSimple CMS admin directory
<Directory /path/to/getsimple/admin>
    Order Deny,Allow
    Deny from all
    Allow from 192.168.1.0/24
    Allow from 10.0.0.0/8
</Directory>