CVE-2022-25765: Pdfkit Command Injection Vulnerability

CVE-2022-25765 Overview

CVE-2022-25765 is a command injection vulnerability affecting the PDFKit Ruby gem. The package, starting from version 0.0.0, fails to properly sanitize URLs before passing them to underlying system commands. This allows attackers to inject arbitrary shell commands through specially crafted URL parameters, potentially leading to complete system compromise.

Critical Impact

Remote attackers can execute arbitrary commands on the server by exploiting improper URL sanitization in PDFKit, potentially leading to full system compromise without requiring authentication.

Affected Products

• PDFKit Ruby gem (all versions from 0.0.0)
• Fedora 35 (packages containing vulnerable PDFKit)
• Fedora 36 (packages containing vulnerable PDFKit)
• Fedora 37 (packages containing vulnerable PDFKit)

Discovery Timeline

• September 9, 2022 - CVE-2022-25765 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-25765

Vulnerability Analysis

This vulnerability stems from inadequate input validation when processing URLs in the PDFKit library. PDFKit is a Ruby gem that wraps the wkhtmltopdf binary, which converts HTML content to PDF documents. When a URL is passed to PDFKit for PDF generation, the library constructs a command-line string that is executed by the system shell.

The vulnerability exists because the URL parameter is not properly sanitized before being incorporated into the shell command. An attacker can craft a malicious URL containing shell metacharacters and command sequences that will be interpreted and executed by the underlying shell when PDFKit processes the request.

Root Cause

The root cause is insufficient input sanitization in the URL handling logic within pdfkit.rb and source.rb. When PDFKit receives a URL to convert, it passes this value directly to the wkhtmltopdf command without adequately escaping or validating the input for shell-special characters. This allows an attacker to break out of the intended URL context and inject arbitrary shell commands using techniques such as command substitution or command chaining.

Attack Vector

The attack vector is network-based, requiring no privileges or user interaction. An attacker can exploit this vulnerability by sending a specially crafted HTTP request to an application that uses PDFKit for PDF generation. The malicious payload is typically embedded within a URL parameter that contains shell metacharacters.

For example, an attacker could inject commands by including backticks, semicolons, or other command separators within the URL parameter. When the vulnerable application passes this URL to PDFKit, the injected commands are executed with the privileges of the web application process.

The vulnerability mechanism involves:

1. A web application accepting user-supplied URL input
2. The URL being passed to PDFKit for PDF conversion
3. PDFKit constructing a shell command with the unsanitized URL
4. The shell interpreting and executing any injected commands

For detailed technical analysis and exploitation details, see the Snyk Vulnerability Report and the Packet Storm Advisory.

Detection Methods for CVE-2022-25765

Indicators of Compromise

• Unusual child processes spawned by Ruby or wkhtmltopdf processes
• Unexpected outbound network connections from application servers
• Log entries containing URLs with shell metacharacters such as backticks, semicolons, pipes, or $() patterns
• Presence of suspicious files or modifications in web application directories

Detection Strategies

• Monitor application logs for URLs containing shell metacharacters or command injection patterns
• Implement Web Application Firewall (WAF) rules to detect and block requests with shell injection payloads in URL parameters
• Use runtime application self-protection (RASP) solutions to detect command execution attempts
• Deploy endpoint detection and response (EDR) solutions to identify suspicious process execution chains

Monitoring Recommendations

• Enable detailed logging for all PDF generation operations in applications using PDFKit
• Set up alerts for unexpected process execution originating from Ruby application contexts
• Monitor for unusual file system activity in directories accessible to the web application
• Implement network-level monitoring to detect potential command-and-control communications following exploitation

How to Mitigate CVE-2022-25765

Immediate Actions Required

• Audit all applications using the PDFKit Ruby gem to identify exposure
• Update PDFKit to a patched version that properly sanitizes URL inputs
• Implement strict input validation on all user-supplied URLs before passing to PDFKit
• Consider using allow-lists for URL schemes and domains where possible

Patch Information

Organizations should update to a patched version of the PDFKit gem. Fedora users should apply the security updates announced through the Fedora Package Announcements. Check the vendor repository and security advisories for the latest patched version information.

Workarounds

• Implement server-side URL validation to reject any input containing shell metacharacters before processing with PDFKit
• Use a sandboxed environment or container with restricted permissions for PDF generation operations
• Disable or restrict PDF generation features that accept user-supplied URLs until patching is complete
• Consider using alternative PDF generation libraries that do not rely on shell command execution

# Example: Add input validation before PDFKit processing
# Validate URLs match expected patterns before use
# Block characters: ` ; | & $ ( ) { } [ ] < > \ " '