CVE-2017-6842 in PoDoFo
Summary
by MITRE
The ColorChanger::GetColorFromStack function in colorchanger.cpp in PoDoFo 0.9.5 allows remote attackers to cause a denial of service (NULL pointer dereference) via a crafted file.
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Analysis
by VulDB Data Team • 09/09/2020
The vulnerability identified as CVE-2017-6842 resides within the PoDoFo library version 0.9.5, specifically within the ColorChanger::GetColorFromStack function located in the colorchanger.cpp source file. This flaw represents a classic null pointer dereference vulnerability that can be exploited by remote attackers to execute a denial of service attack against systems processing PDF documents. The issue manifests when the library encounters a specially crafted PDF file that triggers an unexpected execution path leading to dereferencing a null pointer during color processing operations.
The technical implementation of this vulnerability stems from inadequate input validation and error handling within the color conversion routines of the PoDoFo library. When processing malformed PDF content, particularly in color space definitions or color stack operations, the GetColorFromStack function fails to properly validate pointer references before attempting to access them. This failure aligns with CWE-476, which specifically addresses null pointer dereference vulnerabilities, and represents a fundamental flaw in defensive programming practices. The vulnerability is particularly concerning because it can be triggered through remote file processing, making it exploitable in web applications, document processing services, or any system that accepts and processes PDF files without proper sanitization.
The operational impact of CVE-2017-6842 extends beyond simple service disruption as it can affect a wide range of applications built on top of the PoDoFo library including document management systems, PDF viewers, content management platforms, and any software that processes PDF documents for rendering or manipulation. Attackers can craft malicious PDF files that, when opened or processed by vulnerable applications, will cause the application to crash or become unresponsive. This denial of service condition can be particularly damaging in enterprise environments where PDF processing is a critical component of business operations, potentially leading to complete system unavailability or requiring manual intervention to restore services.
From a cybersecurity perspective, this vulnerability maps to several ATT&CK techniques including T1499.004 for endpoint denial of service and T1059.007 for script execution through command-line interfaces. The attack surface is broad as any application utilizing PoDoFo 0.9.5 for PDF processing is potentially vulnerable, including web applications, desktop software, and server-side document processing services. Organizations should prioritize patching this vulnerability as it represents a low-effort, high-impact attack vector that can be automated and does not require special privileges or advanced exploitation techniques. The vulnerability also highlights the importance of proper input validation and defensive programming practices in document processing libraries, as similar flaws may exist in other components of the same software ecosystem.
Mitigation strategies should include immediate patching of the PoDoFo library to version 0.9.6 or later where this vulnerability has been addressed. Additionally, organizations should implement input sanitization measures including PDF validation, content filtering, and sandboxed processing environments for untrusted documents. Network-level protections such as intrusion detection systems can help detect exploitation attempts, while application-level protections including proper error handling and graceful degradation mechanisms can minimize the impact of successful attacks. Regular security assessments and vulnerability scanning should be conducted to identify other potential weaknesses in document processing pipelines, particularly focusing on memory safety issues and input validation gaps that could lead to similar remote code execution or denial of service conditions.