CVE-2016-8674 in MuPDF
Summary
by MITRE
The pdf_to_num function in pdf-object.c in MuPDF before 1.10 allows remote attackers to cause a denial of service (use-after-free and application crash) via a crafted file.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/15/2020
The vulnerability identified as CVE-2016-8674 resides within the MuPDF document processing library, specifically in the pdf_to_num function located in the pdf-object.c file. This flaw represents a classic use-after-free vulnerability that can be exploited by remote attackers to execute denial of service attacks against systems processing PDF documents. The issue affects MuPDF versions prior to 1.10, making it a significant concern for organizations that rely on this lightweight PDF rendering library for document handling and processing.
The technical implementation of this vulnerability stems from improper memory management within the pdf_to_num function which processes PDF objects during document parsing. When a maliciously crafted PDF file is processed, the function fails to properly validate or handle certain object references, leading to a scenario where memory allocated to a PDF object is freed while still being referenced elsewhere in the code execution path. This use-after-free condition creates a predictable crash pattern that can be reliably exploited by attackers to cause application instability and complete system service disruption.
From an operational impact perspective, this vulnerability presents a serious risk to any system that processes untrusted PDF content, including web applications, email servers, document management systems, and security scanning tools. The remote exploitation capability means that attackers can trigger the vulnerability without requiring local access or authentication, making it particularly dangerous in networked environments where PDF files are frequently processed. The resulting application crash can lead to complete service interruption, potentially allowing for more sophisticated attacks if the system does not properly handle the crash conditions.
The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software implementations, and demonstrates characteristics consistent with ATT&CK technique T1203, which involves exploiting weaknesses in software to gain unauthorized access or cause service disruption. Organizations should prioritize patching affected systems and implementing proper input validation for PDF processing components to prevent exploitation. Additionally, deploying network segmentation and content filtering mechanisms can help mitigate the risk of remote exploitation while patches are being deployed across the environment.
Mitigation strategies should include immediate application of the official MuPDF 1.10 update or newer versions that contain the memory management fixes. System administrators should also consider implementing sandboxing techniques for PDF processing, utilizing automated threat intelligence feeds to identify malicious PDF samples, and establishing robust monitoring for application crash patterns that may indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper memory management in document processing libraries and the potential for seemingly minor implementation flaws to result in significant operational disruptions.