CVE-2026-23907: Apache PDFBox Path Traversal Vulnerability

CVE-2026-23907 Overview

A path traversal vulnerability (CWE-22) exists in the ExtractEmbeddedFiles example code within Apache PDFBox. The vulnerability occurs because the filename obtained from PDComplexFileSpecification.getFilename() is directly appended to the extraction path without proper validation. This allows an attacker to craft a malicious PDF file with embedded files containing path traversal sequences (such as ../) that, when extracted, could write files to arbitrary locations outside the intended extraction directory.

Critical Impact

Attackers can potentially overwrite sensitive system files or place malicious executables in sensitive directories by exploiting this path traversal vulnerability in applications that have copied the vulnerable example code.

Affected Products

• Apache PDFBox versions 2.0.24 through 2.0.35
• Apache PDFBox versions 3.0.0 through 3.0.6
• Any production applications that have copied the vulnerable ExtractEmbeddedFiles example code

Discovery Timeline

• 2026-03-10 - CVE-2026-23907 published to NVD
• 2026-03-11 - Last updated in NVD database

Technical Details for CVE-2026-23907

Vulnerability Analysis

This path traversal vulnerability affects the ExtractEmbeddedFiles example in Apache PDFBox. The core issue lies in how the example code handles filenames from embedded files within PDF documents. When extracting embedded files, the code retrieves the filename using PDComplexFileSpecification.getFilename() and directly concatenates it with the target extraction directory path.

The vulnerability is classified as CWE-22 (Improper Limitation of a Pathname to a Restricted Directory). An attacker can craft a malicious PDF document containing embedded files with specially crafted filenames that include directory traversal sequences like ../ or absolute paths. When such a document is processed by an application using the vulnerable example code, the extracted files can be written outside the intended extraction directory.

The impact includes potential unauthorized file writes to arbitrary filesystem locations, which could lead to configuration file tampering, code injection through overwriting executable files, or data corruption.

Root Cause

The root cause is insufficient input validation when processing embedded file specifications from PDF documents. The example code trusted user-controlled input (the embedded filename from the PDF) without sanitizing or validating that the resulting extraction path remained within the intended directory boundary. The fix implemented by Apache converts both the initial path and extraction paths to canonical paths, then verifies that the extraction path contains the initial path as a prefix, effectively preventing directory escape attempts.

Attack Vector

The attack vector is network-based, requiring an attacker to deliver a maliciously crafted PDF document to a victim application. The attacker embeds files within the PDF that have manipulated filenames containing path traversal sequences. When the victim application processes this PDF using code derived from the vulnerable ExtractEmbeddedFiles example, the embedded files are written to attacker-controlled locations on the filesystem.

The attack requires no authentication or user interaction beyond normal PDF processing operations. The attacker must craft a PDF with embedded files where the filename specification contains directory traversal payloads, such as ../../etc/cron.d/malicious on Unix systems or ..\..\..\Windows\Temp\malicious.exe on Windows systems.

Detection Methods for CVE-2026-23907

Indicators of Compromise

• PDF files containing embedded file specifications with unusual path characters such as .., /, or \ in filenames
• Unexpected file creation events outside designated extraction directories during PDF processing
• Files appearing in sensitive system directories that correlate with PDF processing activity
• Log entries showing file write operations with path traversal sequences in the target path

Detection Strategies

• Implement file integrity monitoring on sensitive directories to detect unauthorized writes during PDF processing
• Deploy application-level logging that captures the full path of files extracted from PDF documents
• Use static code analysis tools to identify any usage of the vulnerable ExtractEmbeddedFiles pattern in your codebase
• Monitor for PDF files being processed that contain embedded file specifications with suspicious filename patterns

Monitoring Recommendations

• Enable detailed audit logging for file creation operations in production environments processing PDF documents
• Configure alerts for any file writes outside expected extraction directories
• Review application logs for path normalization failures or security exceptions during embedded file extraction

How to Mitigate CVE-2026-23907

Immediate Actions Required

• Review your codebase for any instances where the ExtractEmbeddedFiles example code has been copied or adapted
• Update Apache PDFBox to a patched version that includes the corrected example code
• Implement path canonicalization and validation in any custom PDF embedded file extraction logic
• Temporarily disable embedded file extraction functionality if immediate patching is not feasible

Patch Information

Apache has released updated versions of PDFBox that include a corrected ExtractEmbeddedFiles example. The fix converts both the initial extraction path and the computed extraction path to canonical paths, then verifies that the extraction path starts with the initial path. Organizations should update to patched versions and review the Apache Mailing List Thread for additional details. The OpenWall OSS-Security Discussion also provides context on the vulnerability disclosure.

Workarounds

• Implement manual path validation by converting file paths to canonical form and verifying they remain within the intended directory
• Strip all directory components from embedded filenames before extraction, using only the base filename
• Run PDF processing in a sandboxed environment or container with restricted filesystem access
• Apply filesystem-level permissions to prevent writes outside designated extraction directories

# Configuration example
# Example: Restrict extraction directory permissions on Linux
mkdir -p /var/pdfbox/extracted
chmod 700 /var/pdfbox/extracted
chown pdfbox-service:pdfbox-service /var/pdfbox/extracted

# Consider using a chroot or container for PDF processing
# to limit filesystem access scope