CVE-2026-7233 in MuPDF
Summary
by MITRE • 04/28/2026
A vulnerability was determined in Artifex MuPDF up to 1.28.0. The impacted element is the function fz_subset_cff_for_gids of the file subset-cff.c of the component CFF Index Handler. This manipulation causes out-of-bounds read. The attack can only be executed locally. The exploit has been publicly disclosed and may be utilized. The project was informed of the problem early through a bug report but has not responded yet.
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Analysis
by VulDB Data Team • 05/08/2026
The vulnerability in Artifex MuPDF version 1.28.0 and earlier affects the CFF Index Handler component through a critical flaw in the fz_subset_cff_for_gids function located in subset-cff.c. This out-of-bounds read vulnerability represents a significant security risk that could potentially allow attackers to access memory locations beyond the intended buffer boundaries. The flaw specifically manifests when processing CFF (Compact Font Format) index data structures, which are commonly used in PDF documents for font rendering and text display operations. The vulnerability's impact is particularly concerning given that it affects a core font handling mechanism that is extensively used across various PDF processing applications and systems.
The technical nature of this vulnerability stems from inadequate bounds checking within the font subset processing logic. When the fz_subset_cff_for_gids function processes glyph indices for font subset operations, it fails to properly validate array access boundaries, leading to memory access violations that can result in information disclosure, application crashes, or potentially more severe consequences depending on the execution context. This type of vulnerability aligns with CWE-129, which specifically addresses insufficient validation of length fields, and represents a classic example of improper input validation that can lead to memory corruption issues. The vulnerability's classification as an out-of-bounds read places it within the broader category of memory safety issues that have been extensively documented in the cybersecurity community and are often exploited in advanced persistent threat campaigns.
The operational impact of this vulnerability is substantial, particularly given that it has been publicly disclosed and may be actively utilized by threat actors. While the attack requires local execution privileges, this limitation does not diminish the severity of the issue, as local privilege escalation scenarios can often be leveraged to achieve remote code execution through various attack chains. The fact that the project was informed through a bug report but has not yet responded indicates a potential delay in security patching that could leave numerous systems vulnerable. This vulnerability affects not only the core MuPDF library but also any applications that depend on it for PDF processing, including web browsers, document viewers, and content management systems. The public disclosure of the exploit increases the likelihood of exploitation in real-world scenarios, making prompt remediation essential for maintaining system integrity and preventing potential data breaches or service disruptions.
Organizations utilizing Artifex MuPDF should implement immediate mitigations while awaiting official patches from the project maintainers. The recommended approach includes updating to the latest stable version of MuPDF where the vulnerability has been addressed, implementing network segmentation to limit local access to affected systems, and monitoring for suspicious activities that may indicate exploitation attempts. Security teams should also consider deploying intrusion detection systems that can identify patterns associated with out-of-bounds read exploitation attempts. Additionally, application developers should review their code for similar patterns in font processing logic and implement proper bounds checking mechanisms. The vulnerability demonstrates the importance of maintaining up-to-date security practices and the critical need for responsive vulnerability management processes, as highlighted in the ATT&CK framework's defense evasion and execution techniques that often leverage such memory corruption vulnerabilities for unauthorized access to system resources.