CVE-2026-7233 Overview
A vulnerability has been identified in Artifex MuPDF up to version 1.28.0. The affected component is the function fz_subset_cff_for_gids within the file subset-cff.c of the CFF Index Handler. This manipulation causes an out-of-bounds read condition. The attack requires local access to exploit. The vulnerability has been publicly disclosed and proof-of-concept code is available. The project was informed of the problem early through a bug report but has not responded yet.
Critical Impact
Local attackers with low privileges can trigger an out-of-bounds read in MuPDF's CFF font handling code, potentially leading to information disclosure from process memory.
Affected Products
- Artifex MuPDF versions up to 1.28.0
- Applications and systems utilizing MuPDF for PDF rendering
- Document processing pipelines leveraging MuPDF libraries
Discovery Timeline
- 2026-04-28 - CVE-2026-7233 published to NVD
- 2026-04-29 - Last updated in NVD database
Technical Details for CVE-2026-7233
Vulnerability Analysis
This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the CFF (Compact Font Format) Index Handler, specifically within the fz_subset_cff_for_gids function located in subset-cff.c. When processing malformed CFF font data embedded in PDF documents, the function fails to properly validate index boundaries before reading memory, resulting in an out-of-bounds read condition.
The attack requires local access and low privileges to execute. While the immediate impact is limited to information disclosure (confidentiality breach), the exposure of process memory contents could potentially reveal sensitive data or internal application state.
Root Cause
The root cause lies in insufficient bounds checking within the CFF index loading mechanism. When the fz_subset_cff_for_gids function processes glyph identifiers for font subsetting operations, it does not adequately validate that the requested index values fall within the allocated buffer boundaries. This allows an attacker to craft a malicious CFF font structure that references memory locations outside the intended buffer.
Attack Vector
Exploitation requires local access to the target system. An attacker would need to craft a malicious PDF document containing specially constructed CFF font data and convince a user or automated process to open it using an application that relies on the vulnerable MuPDF library. Upon parsing the malformed CFF index structure, the vulnerable function reads beyond allocated memory boundaries.
The attack scenario typically involves:
- Creating a PDF with maliciously crafted CFF font data
- Delivering the PDF to a system running vulnerable MuPDF versions
- Triggering the out-of-bounds read when the document is processed
- Potentially extracting sensitive information from leaked memory contents
For technical details and proof-of-concept information, refer to the GitHub PoC for MuPDF repository.
Detection Methods for CVE-2026-7233
Indicators of Compromise
- Unexpected crashes or memory access violations in MuPDF-based applications when processing PDF files
- PDF documents containing unusual or malformed CFF font structures
- Memory dumps or core files showing out-of-bounds access patterns in subset-cff.c
Detection Strategies
- Monitor for abnormal memory access patterns in processes using MuPDF libraries
- Implement file integrity monitoring for PDF documents entering the environment
- Deploy endpoint detection solutions capable of identifying memory corruption exploitation attempts
- Scan incoming PDF files for malformed CFF font structures before processing
Monitoring Recommendations
- Enable detailed logging for PDF processing applications using MuPDF
- Monitor system logs for segmentation faults or memory access violations related to MuPDF processes
- Implement application-level crash reporting to identify potential exploitation attempts
- Review file upload logs for suspicious PDF documents targeting document processing systems
How to Mitigate CVE-2026-7233
Immediate Actions Required
- Inventory all systems and applications using Artifex MuPDF version 1.28.0 or earlier
- Review the Ghostscript Bug Report #709328 for vendor updates
- Consider restricting PDF processing to trusted sources until a patch is available
- Implement application sandboxing for MuPDF-based document viewers
Patch Information
As of the last update, the Artifex project has been notified of this vulnerability through a bug report but has not yet responded with a patch. Organizations should monitor the Artifex Security Information page and the Ghostscript Bug Report #709328 for updates on an official fix.
Additional vulnerability tracking information is available at VulDB Vulnerability #359840.
Workarounds
- Disable or restrict CFF font processing in MuPDF configurations where possible
- Process untrusted PDF documents in isolated sandbox environments
- Implement strict input validation for PDF files before passing to MuPDF
- Consider alternative PDF libraries for processing untrusted documents until a patch is released
- Apply defense-in-depth measures such as ASLR and DEP to limit exploitation impact
# Example: Running MuPDF-based applications in a restricted environment
# Use firejail or similar sandboxing tools to limit potential impact
firejail --private --net=none --no3d mupdf document.pdf
# Alternatively, use seccomp-bpf filtering for MuPDF processes
# to restrict system calls available to the process
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
