CVE-2017-15369 in MuPDF
Summary
by MITRE
The build_filter_chain function in pdf/pdf-stream.c in Artifex MuPDF before 2017-09-25 mishandles a certain case where a variable may reside in a register, which allows remote attackers to cause a denial of service (Fitz fz_drop_imp use-after-free and application crash) or possibly have unspecified other impact via a crafted PDF document.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 01/03/2023
The vulnerability identified as CVE-2017-15369 resides within the Artifex MuPDF library's pdf-stream.c component, specifically in the build_filter_chain function that processes PDF document streams. This flaw represents a classic use-after-free vulnerability that can be exploited remotely through maliciously crafted PDF files. The issue manifests when the function fails to properly handle a scenario where a variable is stored in a register rather than memory, creating a condition where freed memory may be accessed or manipulated. The vulnerability affects all versions of MuPDF prior to the 2017-09-25 release, making it a significant concern for systems that process untrusted PDF content. According to CWE-416, this vulnerability falls under the category of improper free, where a pointer is used after it has been freed, and potentially relates to CWE-125 for out-of-bounds read conditions that could occur during memory management operations.
The technical exploitation of this vulnerability occurs when a crafted PDF document triggers the build_filter_chain function with specific parameters that cause the variable in question to be allocated to a register. During normal execution flow, when the program attempts to free memory associated with this register-stored variable, the subsequent access patterns may result in memory corruption. This condition can be leveraged by attackers to cause a denial of service through application crashes or potentially achieve more severe outcomes including arbitrary code execution depending on the memory layout and exploitation circumstances. The Fitz fz_drop_imp function mentioned in the vulnerability description is part of MuPDF's internal memory management system, where improper handling of reference counts or object lifecycle management leads to the use-after-free condition. This aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1203 for Exploitation for Client Execution, as the vulnerability enables remote code execution through PDF processing.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially allow attackers to compromise systems that process PDF documents without proper user interaction. Systems most at risk include email servers, web applications, and document management systems that automatically process PDF attachments or content. The vulnerability's remote exploitability means that simply opening or rendering a malicious PDF file could trigger the flaw, making it particularly dangerous in enterprise environments where PDF processing is common. Organizations using older versions of MuPDF libraries are particularly vulnerable, as the fix requires updating to the patched version released on 2017-09-25. The memory corruption resulting from this vulnerability can manifest as application crashes, data corruption, or in some cases, privilege escalation scenarios that could allow attackers to gain unauthorized access to systems. Security professionals should consider implementing PDF content filtering and sandboxing measures as additional defensive controls while awaiting patch deployment. This vulnerability demonstrates the critical importance of proper memory management in document processing libraries and highlights the need for comprehensive testing of edge cases in memory handling functions.