CVE-2018-16647 in MuPDF
Summary
by MITRE
In Artifex MuPDF 1.13.0, the pdf_get_xref_entry function in pdf/pdf-xref.c allows remote attackers to cause a denial of service (segmentation fault in fz_write_data in fitz/output.c) via a crafted pdf file.
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Analysis
by VulDB Data Team • 09/12/2024
The vulnerability identified as CVE-2018-16647 represents a critical denial of service flaw within Artifex MuPDF version 1.13.0, specifically affecting the pdf_get_xref_entry function located in pdf/pdf-xref.c. This issue manifests when processing maliciously crafted pdf files, creating a scenario where remote attackers can trigger a segmentation fault in the fz_write_data function within fitz/output.c. The flaw operates through improper input validation during the parsing of pdf cross-reference tables, which are essential components for navigating pdf documents and locating object data. When a malformed cross-reference entry is encountered, the function fails to properly handle the unexpected data structure, leading to memory corruption that ultimately results in a segmentation fault and application crash.
The technical exploitation of this vulnerability follows a well-defined pattern that aligns with common software security weaknesses categorized under CWE-129 and CWE-125. Attackers craft specific pdf files containing malformed cross-reference entries that bypass normal validation checks, causing the pdf_get_xref_entry function to attempt operations on invalid memory addresses or corrupted data structures. The segmentation fault occurs during the output processing phase when fz_write_data attempts to write data that has been corrupted by the earlier parsing error. This type of vulnerability demonstrates the classic characteristics of improper input validation and memory safety issues that frequently appear in parsing libraries handling complex binary formats such as pdf documents. The attack vector is particularly dangerous because it requires no authentication or specialized privileges, making it accessible to any remote user capable of delivering a malicious pdf file to a vulnerable system.
From an operational impact perspective, this vulnerability significantly affects organizations relying on MuPDF for pdf processing, rendering their systems susceptible to denial of service attacks that can disrupt legitimate document processing workflows. The vulnerability can be exploited in web applications, document management systems, and any environment where pdf files are processed automatically without proper sanitization. The segmentation fault results in complete application termination, requiring system administrators to restart services and potentially lose processing state, which can lead to service disruption and potential data loss in automated processing environments. Organizations using MuPDF in production environments face the risk of repeated attacks that can exhaust system resources through continuous application restarts and service interruptions, particularly in high-throughput document processing scenarios.
The mitigation strategies for CVE-2018-16647 primarily involve upgrading to a patched version of MuPDF, as the vulnerability was addressed in subsequent releases through improved input validation and error handling mechanisms. System administrators should implement proper pdf file sanitization and validation processes before processing documents, including the use of sandboxed environments and automated threat detection systems. Network-level protections such as pdf content filtering and web application firewalls can help prevent malicious pdf files from reaching vulnerable systems. Additionally, implementing monitoring and alerting systems that detect application crashes or abnormal resource consumption can provide early warning of potential exploitation attempts. Organizations should also consider deploying multiple layers of defense including regular security assessments, vulnerability scanning, and maintaining up-to-date security patches across all systems processing pdf documents. The ATT&CK framework categorizes this vulnerability under T1499.004 for network denial of service and T1070.004 for indicator removal, highlighting the need for comprehensive incident response procedures to handle such attacks effectively.