CVE-2020-29599: ImageMagick RCE Vulnerability

CVE-2020-29599 Overview

CVE-2020-29599 is a command injection vulnerability affecting ImageMagick before version 6.9.11-40 and 7.x before 7.0.10-40. The vulnerability exists in how ImageMagick mishandles the -authenticate option, which is used to set passwords for password-protected PDF files. The user-controlled password was not properly escaped or sanitized, allowing attackers to inject additional shell commands via the coders/pdf.c component.

Critical Impact

Successful exploitation allows an attacker to execute arbitrary shell commands on the target system with the privileges of the user running ImageMagick, potentially leading to complete system compromise.

Affected Products

• ImageMagick versions prior to 6.9.11-40
• ImageMagick 7.x versions prior to 7.0.10-40
• Debian Linux 9.0 (Stretch)

Discovery Timeline

• 2020-12-07 - CVE-2020-29599 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-29599

Vulnerability Analysis

This command injection vulnerability (CWE-91) resides in ImageMagick's PDF processing functionality, specifically within the coders/pdf.c file. When processing password-protected PDF files, ImageMagick accepts user input through the -authenticate command-line option to provide the PDF password. The implementation fails to properly sanitize or escape this user-controlled input before passing it to shell commands.

The vulnerability requires local access and user interaction—an attacker must convince a user to process a crafted PDF file or execute ImageMagick with a malicious password argument. Despite requiring user interaction, successful exploitation grants the attacker high impact across confidentiality, integrity, and availability, as they can execute arbitrary commands with the same privileges as the ImageMagick process.

Root Cause

The root cause of CVE-2020-29599 lies in insufficient input validation and improper handling of shell metacharacters. The -authenticate parameter value is passed directly to shell command construction without adequate sanitization. Special characters such as backticks, semicolons, and other shell metacharacters are not escaped, allowing an attacker to break out of the intended command context and inject additional malicious commands.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to either have local access to the system or social engineer a user into processing a malicious PDF file. An attacker can craft a specially formatted password string containing shell metacharacters that, when processed by ImageMagick, results in the execution of arbitrary commands. For example, using command substitution syntax or command separators within the password parameter allows injection of additional shell commands that execute alongside or instead of the intended PDF password handling logic.

The vulnerability can be exploited in scenarios where ImageMagick processes PDF files from untrusted sources, such as web applications that perform image conversion or thumbnail generation. Technical details about the exploitation mechanism are available in the Blog on ImageMagick Shell Injection.

Detection Methods for CVE-2020-29599

Indicators of Compromise

• Unusual process spawning from ImageMagick processes (e.g., convert, identify, mogrify spawning shell commands)
• PDF processing operations containing unexpected shell metacharacters in authentication parameters
• Anomalous network connections or file system activities originating from ImageMagick processes

Detection Strategies

• Monitor command-line arguments passed to ImageMagick binaries for shell metacharacters in -authenticate parameters
• Implement process monitoring to detect unexpected child processes spawned by ImageMagick components
• Use application-level logging to track all PDF processing operations with authentication parameters
• Deploy runtime application self-protection (RASP) solutions to detect command injection attempts

Monitoring Recommendations

• Enable verbose logging for all ImageMagick operations in production environments
• Configure SIEM rules to alert on command-line patterns containing shell injection indicators
• Monitor for unusual system calls from processes associated with image processing
• Implement file integrity monitoring for ImageMagick configuration files and policy settings

How to Mitigate CVE-2020-29599

Immediate Actions Required

• Upgrade ImageMagick to version 6.9.11-40 or later for the 6.x branch
• Upgrade ImageMagick to version 7.0.10-40 or later for the 7.x branch
• Review and restrict ImageMagick's policy.xml to disable PDF processing if not required
• Avoid processing PDF files from untrusted sources until patching is complete

Patch Information

The vulnerability has been addressed in ImageMagick versions 6.9.11-40 and 7.0.10-40. Security advisories and patch information are available from multiple sources including Debian LTS Security Announcement and Gentoo GLSA 202101-36. Users should update to the latest available version through their distribution's package manager or compile from source using the ImageMagick GitHub repository.

Workarounds

• Disable PDF coders entirely in the ImageMagick policy.xml configuration file
• Sanitize all user input before passing it to ImageMagick command-line tools
• Run ImageMagick processes in sandboxed environments with minimal privileges
• Implement strict input validation to reject password parameters containing shell metacharacters

# Disable PDF processing in ImageMagick policy.xml
# Add the following to /etc/ImageMagick-6/policy.xml or /etc/ImageMagick-7/policy.xml

<policy domain="coder" rights="none" pattern="PDF" />
<policy domain="coder" rights="none" pattern="PS" />
<policy domain="coder" rights="none" pattern="EPS" />
<policy domain="coder" rights="none" pattern="XPS" />