CVE-2018-18662 in MuPDF
Summary
by MITRE
There is an out-of-bounds read in fz_run_t3_glyph in fitz/font.c in Artifex MuPDF 1.14.0, as demonstrated by mutool.
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Analysis
by VulDB Data Team • 09/12/2024
The vulnerability identified as CVE-2018-18662 represents a critical out-of-bounds read flaw within the MuPDF document processing library version 1.14.0. This issue specifically affects the fz_run_t3_glyph function located in the fitz/font.c source file, which is responsible for rendering Type 3 font glyphs during document processing. The vulnerability manifests when mutool, a command-line utility included with MuPDF, processes malformed PDF documents containing crafted Type 3 font data. This out-of-bounds read occurs during the font rendering process where the application fails to properly validate array indices or buffer boundaries before accessing memory locations. The flaw stems from inadequate input validation and boundary checking mechanisms within the font processing pipeline, allowing an attacker to craft malicious PDF files that trigger memory access violations when the vulnerable library attempts to render specific font elements. Such vulnerabilities fall under the CWE-125 weakness category, which specifically addresses out-of-bounds read conditions in software implementations. The technical execution of this vulnerability requires an attacker to prepare a specially crafted PDF document containing malformed Type 3 font data that, when processed by MuPDF, causes the application to read memory beyond the allocated buffer boundaries. This type of vulnerability represents a classic memory safety issue that can potentially lead to information disclosure, application crashes, or in more severe cases, arbitrary code execution depending on the system configuration and memory layout. The impact of this vulnerability extends beyond simple document rendering as it affects any application or system that utilizes MuPDF 1.14.0 for PDF processing, including web applications, document viewers, and content management systems. From an operational perspective, this vulnerability creates a significant risk for organizations that process untrusted PDF documents, as it can be exploited through simple document upload mechanisms or automated processing workflows. The ATT&CK framework categorizes this type of vulnerability under the T1059.007 technique, which involves the execution of malicious code through legitimate system processes, and the T1203 technique related to legitimate user execution paths. The vulnerability's exploitation pathway typically involves an attacker uploading a crafted PDF document that triggers the vulnerable code path when the document is opened or processed by any application using the affected MuPDF library version. Security practitioners should consider this vulnerability as part of a broader threat landscape that includes similar memory safety issues commonly found in document processing libraries. The remediation strategy involves upgrading to a patched version of MuPDF that addresses the boundary checking issues in the font processing code, specifically ensuring that array indices are validated before memory access operations occur. Organizations should also implement defensive measures such as input sanitization, restricted document processing environments, and regular security updates to mitigate the risk of exploitation. The vulnerability demonstrates the importance of robust input validation and memory safety practices in document processing libraries, where the complexity of font handling and rendering operations can introduce subtle but critical security flaws that affect widespread software ecosystems.