CVE-2022-50897: mPDF 7.0 Path Traversal Vulnerability

CVE-2022-50897 Overview

mPDF 7.0 contains a local file inclusion (LFI) vulnerability that allows attackers to read arbitrary system files by manipulating annotation file parameters. Attackers can generate URL-encoded or base64 payloads to include local files through crafted annotation content with file path specifications. This vulnerability is classified under CWE-98 (Improper Control of Filename for Include/Require Statement in PHP Program).

Critical Impact

Unauthenticated remote attackers can read sensitive system files such as /etc/passwd, configuration files containing credentials, and application source code through crafted PDF annotation parameters.

Affected Products

• mPDF 7.0

Discovery Timeline

• 2026-01-13 - CVE CVE-2022-50897 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2022-50897

Vulnerability Analysis

This local file inclusion vulnerability exists in mPDF version 7.0's handling of annotation file parameters. The library fails to properly sanitize user-supplied file paths when processing PDF annotations, allowing attackers to traverse directories and include arbitrary local files within the generated PDF output. The vulnerability can be exploited over the network without requiring authentication or user interaction, enabling attackers to exfiltrate sensitive information from the underlying server.

Root Cause

The root cause lies in improper input validation of file path specifications within mPDF's annotation processing functionality. The library does not adequately sanitize or restrict file paths provided through annotation parameters, failing to implement proper allowlists or path canonicalization. This allows attackers to use directory traversal sequences or encoded payloads to reference files outside intended directories.

Attack Vector

The attack is conducted over the network against web applications using the vulnerable mPDF library. An attacker crafts a malicious request containing specially formatted annotation content with file path specifications pointing to sensitive system files. The payload can be URL-encoded or base64-encoded to bypass basic input filters. When the application processes this input with mPDF, the library includes the contents of the specified local files in the generated PDF output, effectively disclosing arbitrary file contents to the attacker.

The vulnerability mechanism involves manipulation of annotation file parameters during PDF generation. Attackers craft payloads containing file path specifications (e.g., ../../../etc/passwd) within annotation content. Technical details and proof-of-concept examples are available in the Exploit-DB #50995 advisory.

Detection Methods for CVE-2022-50897

Indicators of Compromise

• Unusual PDF generation requests containing directory traversal patterns such as ../ or encoded variants (%2e%2e%2f)
• Server logs showing access attempts to sensitive files like /etc/passwd, /etc/shadow, or application configuration files
• PDF outputs containing unexpected file contents or system information
• Web application firewall logs indicating LFI attack patterns targeting mPDF endpoints

Detection Strategies

• Deploy web application firewall rules to detect and block directory traversal patterns in request parameters
• Implement log monitoring for file access attempts outside expected directories during PDF generation
• Use intrusion detection systems configured to alert on LFI attack signatures
• Monitor for anomalous PDF generation activity including unusual file sizes or processing times

Monitoring Recommendations

• Enable detailed logging for all PDF generation operations including input parameters
• Configure file integrity monitoring for sensitive system files and application configurations
• Implement real-time alerting for detected traversal patterns in web application inputs
• Review PDF generation logs periodically for suspicious file path patterns

How to Mitigate CVE-2022-50897

Immediate Actions Required

• Upgrade mPDF to the latest patched version if available
• Implement input validation to sanitize all user-supplied data before passing to mPDF
• Deploy web application firewall rules to block LFI attack patterns
• Restrict file system permissions for the web server user to limit accessible files

Patch Information

Organizations should consult the official mPDF Documentation for information on patched versions. Additionally, review the VulnCheck Advisory for specific remediation guidance. If no patch is available, implement the workarounds listed below until an official fix is released.

Workarounds

• Implement strict input validation and sanitization for all user-controlled data passed to mPDF annotation functions
• Use allowlist-based validation to restrict permitted file paths and reject any directory traversal sequences
• Run the web application with minimal file system privileges to limit the impact of successful exploitation
• Consider disabling annotation functionality if not required by your application

# Example PHP input sanitization
# Validate and sanitize file paths before passing to mPDF
# Remove directory traversal sequences and validate against allowlist
# Implement in your application before calling mPDF methods