CVE-2024-56378: Poppler Out-of-Bounds Read Vulnerability

CVE-2024-56378 Overview

CVE-2024-56378 is an out-of-bounds read vulnerability discovered in libpoppler.so, a widely-used PDF rendering library. The vulnerability exists within the JBIG2Bitmap::combine function in JBIG2Stream.cc, affecting Poppler versions through 24.12.0. This memory safety issue could allow attackers to read data beyond allocated buffer boundaries when processing specially crafted PDF documents containing malicious JBIG2 image streams.

Critical Impact

Attackers exploiting this vulnerability via malicious PDF documents could potentially read sensitive memory contents or cause application instability in PDF processing applications.

Affected Products

• Freedesktop Poppler versions through 24.12.0
• Applications using libpoppler.so for PDF rendering
• Linux distributions shipping vulnerable Poppler versions (including Debian LTS)

Discovery Timeline

• 2024-12-23 - CVE-2024-56378 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-56378

Vulnerability Analysis

The vulnerability resides in the JBIG2 image decoding functionality of Poppler, specifically within the JBIG2Bitmap::combine function located in JBIG2Stream.cc. JBIG2 is a bi-level image compression standard commonly used in PDF documents for efficient storage of black-and-white images such as scanned documents.

When processing JBIG2 image segments, the combine function performs bitmap manipulation operations that merge or overlay bitmap data. The out-of-bounds read occurs due to insufficient boundary validation before accessing memory during these bitmap combining operations. An attacker can craft a malicious PDF document with specially constructed JBIG2 stream parameters that cause the function to read beyond the allocated buffer boundaries.

Root Cause

The root cause is classified as CWE-125 (Out-of-bounds Read), stemming from improper input validation in the JBIG2Bitmap::combine function. The function fails to adequately verify that bitmap dimensions and offsets remain within valid memory bounds before performing read operations. This allows malformed JBIG2 segments to trigger reads from unintended memory locations.

Attack Vector

The attack vector is network-based, requiring an attacker to deliver a malicious PDF document to the victim. This can be accomplished through various means including email attachments, web downloads, or embedding PDFs in web content. When the victim opens the crafted PDF using an application that relies on Poppler for rendering (such as document viewers like Evince or Okular), the malicious JBIG2 stream triggers the out-of-bounds read during document parsing.

The vulnerability does not require user authentication and can be exploited with low attack complexity. However, exploitation is limited in scope as it primarily enables unauthorized data reads rather than code execution or system compromise.

The vulnerability manifests during JBIG2 bitmap combination operations when processing malformed PDF documents. Technical details regarding the specific boundary conditions and exploitation mechanism can be found in the GitLab Poppler Issue Discussion.

Detection Methods for CVE-2024-56378

Indicators of Compromise

• Unexpected crashes or memory access violations in PDF viewer applications
• Application logs showing JBIG2 decoding errors or segmentation faults when processing PDF files
• Suspicious PDF documents with anomalous JBIG2 stream structures or malformed segment headers

Detection Strategies

• Monitor PDF processing applications for abnormal memory access patterns or crashes during document rendering
• Implement file inspection rules to identify PDFs with potentially malicious JBIG2 streams
• Deploy application-level monitoring to detect Poppler library crashes or memory access violations
• Use static analysis tools to scan PDF documents for suspicious JBIG2 segment configurations

Monitoring Recommendations

• Enable crash reporting and memory dump analysis for PDF viewing applications using Poppler
• Monitor system logs for repeated crashes in PDF processing workflows
• Implement network traffic inspection to identify potentially malicious PDF downloads
• Configure endpoint detection to alert on suspicious PDF-related process behavior

How to Mitigate CVE-2024-56378

Immediate Actions Required

• Update Poppler to a patched version that includes the fix for CVE-2024-56378
• Review and update all applications that bundle or depend on libpoppler.so
• For Debian LTS users, apply the security updates referenced in the Debian LTS Security Announcement
• Consider temporarily disabling JBIG2 processing if updates cannot be immediately applied

Patch Information

The vulnerability has been addressed by Freedesktop in a commit to the Poppler repository. The fix implements proper boundary checking in the JBIG2Bitmap::combine function to prevent out-of-bounds read operations. Organizations should upgrade to patched versions of Poppler that include commit ade9b5ebed44b0c15522c27669ef6cdf93eff84e. The patch is available in the GitLab Poppler Commit Update.

Workarounds

• Implement strict PDF input validation and sanitization before processing with Poppler
• Use application sandboxing to limit the impact of potential exploitation
• Restrict PDF processing to trusted sources and implement network-level filtering for PDF downloads
• Consider alternative PDF libraries for processing untrusted documents until patches are applied

# Check installed Poppler version on Linux systems
poppler-utils --version
# or
pkg-config --modversion poppler

# Update Poppler on Debian/Ubuntu
sudo apt-get update && sudo apt-get upgrade poppler-utils libpoppler-dev

# Update Poppler on RHEL/CentOS/Fedora
sudo dnf update poppler poppler-utils