CVE-2019-16115 in Xpdf
Summary
by MITRE
In Xpdf 4.01.01, a stack-based buffer under-read could be triggered in IdentityFunction::transform in Function.cc, used by GfxAxialShading::getColor. It can, for example, be triggered by sending a crafted PDF document to the pdftoppm tool. It allows an attacker to use a crafted PDF file to cause Denial of Service or possibly unspecified other impact.
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Analysis
by VulDB Data Team • 12/18/2023
The vulnerability identified as CVE-2019-16115 represents a critical stack-based buffer under-read flaw within the Xpdf library version 4.01.01. This issue manifests specifically within the IdentityFunction::transform method located in Function.cc, which serves as a core component in the PDF rendering process. The vulnerability is particularly concerning because it can be triggered through the GfxAxialShading::getColor function, which is part of the graphics handling subsystem responsible for processing axial shading patterns in PDF documents. When a maliciously crafted PDF file is processed by applications utilizing the pdftoppm tool or other Xpdf-based utilities, the under-read condition occurs during the execution of the transform function, creating a potential exploitation vector for attackers seeking to disrupt normal operations.
The technical nature of this vulnerability places it squarely within the realm of memory safety issues classified under CWE-126, which deals with buffer over-read conditions that can lead to information disclosure, system crashes, or potentially more severe consequences. The stack-based buffer under-read occurs when the program attempts to read memory locations that lie outside the bounds of a stack-allocated buffer, specifically in the context of PDF function processing. This type of vulnerability is particularly dangerous because it can result in unpredictable behavior, including segmentation faults that cause application crashes, or in more sophisticated exploitation scenarios where attackers might leverage the memory access pattern to infer sensitive information from adjacent memory locations. The flaw demonstrates how PDF processing libraries can become attack vectors when they fail to properly validate input parameters during complex mathematical function evaluations used in shading calculations.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially enable more sophisticated attacks depending on the execution environment and the specific implementation details of the affected applications. When the pdftoppm tool or other Xpdf-dependent software processes a crafted PDF document, the under-read condition can cause the application to terminate abruptly, effectively creating a denial of service condition that prevents legitimate users from accessing PDF content. However, the vulnerability's potential for more severe consequences cannot be discounted, particularly in environments where the affected software is used in automated processing pipelines or where attackers might attempt to use the memory access pattern to extract information from adjacent memory regions. The vulnerability affects the broader PDF processing ecosystem since Xpdf is widely used across various security tools, document viewers, and conversion utilities, making the potential impact substantial.
Mitigation strategies for CVE-2019-16115 must focus on both immediate patching and operational security measures to protect against exploitation. The most effective solution involves upgrading to a patched version of the Xpdf library where the buffer under-read condition has been addressed through proper bounds checking and input validation. Organizations should prioritize updating all systems that utilize Xpdf-based tools, including pdftoppm, pdfinfo, and any custom applications that depend on the library. Additionally, implementing defensive programming practices such as input sanitization and validation can provide additional layers of protection, though these measures are secondary to the core patching requirement. Security teams should also consider deploying network-based intrusion detection systems that can identify and block suspicious PDF file transfers that might contain the crafted payloads designed to trigger this vulnerability, as outlined in ATT&CK technique T1059 for command and control communications and T1203 for exploitation of software vulnerabilities. The vulnerability underscores the critical importance of maintaining up-to-date security libraries and implementing robust input validation mechanisms in document processing applications to prevent exploitation of memory safety issues that can have far-reaching consequences across multiple software domains.