CVE-2019-9878 in Xpdf
Summary
by MITRE
There is an invalid memory access in the function GfxIndexedColorSpace::mapColorToBase() located in GfxState.cc in Xpdf 4.0.0, as used in pdfalto 0.2. It can be triggered by (for example) sending a crafted pdf file to the pdftops binary. It allows an attacker to cause Denial of Service (Segmentation fault) or possibly have unspecified other impact.
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Analysis
by VulDB Data Team • 08/04/2023
The vulnerability identified as CVE-2019-9878 represents a critical memory access flaw within the Xpdf library version 4.0.0, specifically within the GfxIndexedColorSpace::mapColorToBase() function located in GfxState.cc. This issue manifests as an invalid memory access condition that can be exploited through crafted PDF files processed by the pdftops binary component of the pdfalto 0.2 utility. The vulnerability demonstrates characteristics consistent with a buffer over-read or improper memory dereference pattern that falls under CWE-125, which describes out-of-bounds read conditions in software implementations. The affected component operates within the graphics state management subsystem of the PDF rendering engine, where color space transformations are performed during document processing.
The technical exploitation of this vulnerability occurs when a malicious PDF file contains specially crafted color space definitions that trigger the mapColorToBase() function with invalid parameters or indices. During execution, the function attempts to access memory locations beyond the allocated bounds of its internal data structures, leading to segmentation faults that cause the application to crash. This behavior constitutes a denial of service condition that can be reliably triggered by an unauthenticated remote attacker who has the ability to submit PDF files to a system running the vulnerable pdfalto utility. The vulnerability's impact extends beyond simple service disruption as the improper memory handling could potentially lead to arbitrary code execution in certain scenarios, though the primary documented impact remains denial of service.
From an operational perspective, this vulnerability presents significant risk to organizations that process untrusted PDF documents through systems utilizing the affected pdfalto utility or similar Xpdf-based applications. The attack surface includes any system that converts PDF files to PostScript or other formats using the pdftops binary, making it particularly dangerous in environments such as document management systems, automated processing pipelines, and web applications that accept PDF uploads. The vulnerability can be exploited in automated attack scenarios where an attacker simply needs to upload a malicious PDF file to trigger the segmentation fault, requiring no specialized knowledge of the underlying system architecture. The ATT&CK framework categorizes this as a privilege escalation or denial of service technique through software exploitation, with potential for lateral movement if the affected system processes documents from multiple sources.
Mitigation strategies for CVE-2019-9878 should prioritize immediate patching of the Xpdf library to version 4.01 or later, which contains the necessary fixes for the memory access violation. Organizations should also implement input validation controls that filter or sanitize PDF files before processing, particularly focusing on color space definitions and indexed color mappings. Network-based defenses can include content filtering solutions that scan PDF attachments for known malicious patterns, though these may not prevent all exploitation attempts. System administrators should consider implementing sandboxing or containerization techniques to isolate PDF processing components, limiting the potential impact of successful exploitation attempts. Additionally, monitoring and logging should be enhanced to detect unusual patterns of segmentation faults or process crashes that may indicate exploitation attempts. The vulnerability demonstrates the importance of proper memory management in PDF rendering engines and highlights the need for comprehensive input validation in document processing systems that handle untrusted content.