CVE-2018-25306: PDFunite Buffer Overflow Vulnerability

CVE-2018-25306 Overview

CVE-2018-25306 is a buffer overflow vulnerability affecting PDFunite version 0.41.0, a command-line utility used for merging PDF files. The vulnerability exists within the XRef::getEntry function in the libpoppler library and can be exploited by local attackers to crash the application through specially crafted PDF files. This denial of service condition occurs when the pdfunite utility attempts to process malformed PDF documents during merge operations.

Critical Impact

Local attackers can cause application crashes and denial of service by supplying maliciously crafted PDF files to the pdfunite utility, triggering a segmentation fault in libpoppler's cross-reference handling code.

Affected Products

• PDFunite 0.41.0
• Poppler library (libpoppler) versions bundled with PDFunite 0.41.0
• Ubuntu poppler-utils package prior to version 0.57.0-2ubuntu4.2

Discovery Timeline

• 2026-04-29 - CVE CVE-2018-25306 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2018-25306

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The flaw resides in the XRef::getEntry function within the libpoppler library, which handles PDF cross-reference table parsing. When processing a malformed PDF file with manipulated cross-reference entries, the function fails to properly validate input boundaries, leading to buffer overflow conditions.

The vulnerability requires local access to exploit, as an attacker must provide a crafted PDF file to the pdfunite command-line utility. While the attack does not require special privileges or user interaction, the impact is limited to high availability disruption through application crashes (segmentation fault). No confidentiality or integrity impacts have been identified, making this primarily a denial of service vulnerability.

Root Cause

The root cause stems from insufficient bounds checking in the XRef::getEntry function when parsing cross-reference (xref) table entries in PDF documents. The function assumes valid input structure and does not adequately validate the size and format of cross-reference entries before copying data into fixed-size buffers. When a PDF file contains maliciously crafted xref entries with unexpected sizes or malformed data, the function writes beyond allocated buffer boundaries, corrupting adjacent memory and causing a segmentation fault.

Attack Vector

The attack vector is local, requiring an attacker to either have direct access to the system or convince a user to process a malicious PDF file. The attack can be executed by:

1. Creating a specially crafted PDF file with malformed cross-reference table entries
2. Providing this file as input to the pdfunite command-line utility
3. The utility invokes libpoppler's PDF parsing routines, which process the xref table
4. The XRef::getEntry function encounters the malformed data and overflows its buffer
5. A segmentation fault occurs, terminating the application

The vulnerability is particularly relevant in automated document processing workflows where untrusted PDF files may be processed without prior validation.

Detection Methods for CVE-2018-25306

Indicators of Compromise

• Unexpected crashes or segmentation faults in pdfunite or applications using libpoppler
• Core dump files generated by PDF processing utilities
• Presence of PDF files with abnormally structured or oversized cross-reference tables
• System logs indicating SIGSEGV signals from poppler-based applications

Detection Strategies

• Monitor for abnormal termination of pdfunite and other poppler-utils binaries with segmentation fault signals
• Implement file integrity monitoring on directories where PDF files are processed
• Deploy application crash monitoring to detect repeated DoS attempts
• Use PDF structure validation tools to identify malformed files before processing

Monitoring Recommendations

• Enable core dump analysis for applications that process PDF files
• Configure system logging to capture application crashes and signals
• Monitor process termination events for poppler-related utilities
• Implement rate limiting on PDF processing endpoints to mitigate DoS impact

How to Mitigate CVE-2018-25306

Immediate Actions Required

• Update the poppler library and poppler-utils package to version 0.57.0-2ubuntu4.2 or later on Ubuntu systems
• Validate PDF files before processing with pdfunite using independent PDF validation tools
• Implement input sanitization for any workflows accepting PDF files from untrusted sources
• Consider running PDF processing utilities in sandboxed environments to contain potential crashes

Patch Information

Ubuntu has released patched versions of the poppler library addressing this vulnerability. Users should update to poppler version 0.57.0-2ubuntu4.2 or later as documented in the Launchpad Poppler Source Package. The poppler-utils package containing pdfunite should also be updated accordingly. For additional technical details, refer to the VulnCheck PDFUnite Advisory and Exploit-DB #44490.

Workarounds

• Avoid processing PDF files from untrusted sources with vulnerable versions of pdfunite
• Implement file size and structure validation before passing PDFs to pdfunite
• Use alternative PDF merging tools that have been patched or are not affected by this vulnerability
• Deploy application sandboxing (e.g., containers, seccomp) to limit the impact of crashes

# Update poppler packages on Ubuntu
sudo apt-get update
sudo apt-get install --only-upgrade poppler-utils libpoppler-glib8

# Verify installed version
dpkg -l | grep poppler