CVE-2023-29689: PyroCMS 3.9 Remote Code Execution (RCE)

CVE-2023-29689 Overview

PyroCMS 3.9 contains a critical remote code execution (RCE) vulnerability that can be exploited through a server-side template injection (SSTI) flaw. This vulnerability allows a malicious attacker to send customized commands to the server and execute arbitrary code on the affected system, potentially leading to complete system compromise.

Critical Impact

Unauthenticated attackers can achieve remote code execution through server-side template injection, allowing complete system takeover with full access to confidential data, system modification capabilities, and potential service disruption.

Affected Products

• PyroCMS version 3.9
• Systems running vulnerable PyroCMS installations
• Web servers hosting PyroCMS 3.9 applications

Discovery Timeline

• 2023-08-04 - CVE-2023-29689 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-29689

Vulnerability Analysis

This vulnerability stems from improper handling of user-supplied input within the template engine used by PyroCMS 3.9. Server-side template injection (SSTI) occurs when an application embeds user input directly into template expressions without proper sanitization. In the case of PyroCMS, the Twig template engine processes malicious payloads that allow attackers to escape the intended template context and execute arbitrary system commands.

The attack requires no authentication and can be performed remotely over the network. Successful exploitation grants attackers the ability to execute arbitrary commands with the privileges of the web server process, potentially compromising confidentiality, integrity, and availability of the target system.

Root Cause

The vulnerability exists due to insufficient input validation and sanitization when processing template data. PyroCMS fails to properly escape or restrict user-controlled input before passing it to the Twig template engine, allowing attackers to inject malicious template directives. When these directives are processed, they can access internal objects and methods that facilitate code execution.

Attack Vector

The attack is network-based and exploits the SSTI vulnerability by injecting specially crafted template expressions into input fields or parameters that are subsequently processed by the template engine. An attacker crafts malicious payloads containing Twig template syntax that, when rendered by the server, executes arbitrary PHP code or system commands.

The exploitation typically follows this pattern:

1. The attacker identifies input fields that are reflected in template output
2. A malicious SSTI payload is crafted using Twig-specific syntax
3. The payload leverages Twig's object access capabilities to reach PHP functions
4. System commands are executed with the web server's privileges

For detailed technical exploitation information, refer to the SSTI to RCE Analysis and Packet Storm Security Exploit documentation.

Detection Methods for CVE-2023-29689

Indicators of Compromise

• Unusual HTTP requests containing Twig template syntax such as {{, {%, or {# in parameter values
• Web server logs showing requests with encoded template injection payloads
• Unexpected process spawning from web server processes (PHP-FPM, Apache, Nginx workers)
• Outbound network connections from web application servers to unknown destinations

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block common SSTI payload patterns
• Monitor web server access logs for suspicious requests containing template engine syntax
• Deploy runtime application self-protection (RASP) solutions to detect template injection attempts
• Use intrusion detection systems (IDS) with signatures for known SSTI exploitation techniques

Monitoring Recommendations

• Enable detailed logging for all HTTP requests to PyroCMS applications
• Monitor system process trees for unexpected child processes spawned by web server workers
• Implement file integrity monitoring on critical PyroCMS configuration and code files
• Set up alerts for unusual resource consumption patterns that may indicate post-exploitation activity

How to Mitigate CVE-2023-29689

Immediate Actions Required

• Audit all PyroCMS 3.9 installations in your environment and identify affected systems
• Implement WAF rules to block requests containing Twig template injection patterns
• Restrict network access to PyroCMS administrative interfaces
• Review web server logs for signs of exploitation attempts or successful compromise

Patch Information

No official vendor patch information is currently available in the CVE data. Organizations should monitor the PyroCMS project for security updates and upgrade to the latest available version that addresses this vulnerability. In the absence of an official patch, implementing the workarounds below is strongly recommended.

Workarounds

• Deploy a Web Application Firewall with rules blocking SSTI payloads and template syntax in user input
• Implement strict input validation on all user-controllable parameters before template processing
• Consider sandboxing the Twig template engine to restrict access to dangerous functions and objects
• Isolate PyroCMS installations using containerization or network segmentation to limit blast radius

# Example WAF rule pattern for ModSecurity to block common SSTI payloads
# Add to your ModSecurity configuration
SecRule ARGS "@rx \{\{.*\}\}" \
    "id:100001,\
    phase:2,\
    deny,\
    status:403,\
    log,\
    msg:'Potential SSTI Attack Detected - Twig Template Syntax'"