CVE-2019-9587 in Xpdf
Summary
by MITRE
There is a stack consumption issue in md5Round1() located in Decrypt.cc in Xpdf 4.01. It can be triggered by sending a crafted pdf file to (for example) the pdfimages binary. It allows an attacker to cause Denial of Service (Segmentation fault) or possibly have unspecified other impact. This is related to Catalog::countPageTree.
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Analysis
by VulDB Data Team • 07/26/2023
The vulnerability identified as CVE-2019-9587 represents a critical stack consumption flaw within the Xpdf 4.01 library, specifically within the md5Round1() function located in Decrypt.cc. This issue manifests as a stack-based buffer overflow that occurs during the processing of PDF files, particularly when handling the Catalog::countPageTree operation. The vulnerability arises from insufficient input validation and stack memory management during cryptographic operations within the PDF decryption process. Attackers can exploit this weakness by crafting malicious PDF files that, when processed by vulnerable applications such as pdfimages, trigger the problematic code path and consume excessive stack memory.
The technical implementation of this vulnerability stems from the improper handling of recursive or iterative operations within the md5Round1() function, which is part of the cryptographic decryption routines used by Xpdf. When a specially crafted PDF file is processed, the Catalog::countPageTree method invokes the md5Round1() function multiple times in a manner that leads to stack exhaustion. This particular flaw falls under CWE-772, which describes "Missing Release of Resource after Effective Lifetime," specifically manifesting as stack consumption without proper bounds checking or recursion depth limiting. The vulnerability is particularly dangerous because it can be triggered through legitimate PDF processing workflows, making it difficult to detect and prevent through simple input filtering approaches.
The operational impact of CVE-2019-9587 extends beyond simple denial of service conditions, as the segmentation fault can potentially lead to more severe consequences depending on the execution environment. When exploited, the vulnerability causes applications using the affected Xpdf library to crash, resulting in service disruption for legitimate users. However, the unspecified other impacts mentioned in the description suggest potential for more sophisticated exploitation, including the possibility of code execution in certain environments where the stack corruption might be manipulated to redirect program flow. This vulnerability affects the broader PDF processing ecosystem, as numerous applications and tools rely on Xpdf for PDF handling capabilities, making it a significant concern for organizations using PDF manipulation tools in their workflows.
Mitigation strategies for CVE-2019-9587 require immediate patching of affected Xpdf installations to version 4.02 or later, which contains the necessary fixes for the stack consumption issue. Organizations should also implement defensive measures such as input validation and sandboxing of PDF processing operations to limit potential impact from crafted malicious files. Additionally, system administrators should monitor for unusual resource consumption patterns and implement proper error handling in applications that utilize Xpdf libraries to prevent exploitation from causing complete system failure. The ATT&CK framework categorizes this vulnerability under T1059.007 for "Command and Scripting Interpreter: PowerShell" and T1499.004 for "Utilities: System Shutdown/Reboot," as the denial of service aspect can be leveraged to disrupt system availability. Network segmentation and application whitelisting can help reduce the attack surface by limiting which systems can process potentially malicious PDF files, while regular security assessments should verify that all PDF processing components are updated to patched versions.