CVE-2017-6840 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 (invalid read) via a crafted file.
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Analysis
by VulDB Data Team • 09/09/2020
The vulnerability identified as CVE-2017-6840 resides within the PoDoFo library version 0.9.5, specifically in the ColorChanger::GetColorFromStack function located in the colorchanger.cpp source file. This flaw represents a classic case of improper input validation that can be exploited by remote attackers to execute denial of service attacks. The vulnerability occurs when the library processes crafted PDF files that contain malformed color data, leading to an invalid memory read operation that ultimately crashes the application.
This security issue falls under the category of memory corruption vulnerabilities and can be classified as CWE-125, which describes an out-of-bounds read condition. The technical implementation flaw stems from insufficient bounds checking within the GetColorFromStack function, where the code fails to properly validate the size and content of color data retrieved from the stack. When processing maliciously crafted PDF documents, the function attempts to access memory locations beyond the allocated buffer boundaries, resulting in an invalid read that terminates the application process. The vulnerability demonstrates characteristics consistent with the attack pattern described in the MITRE ATT&CK framework under the T1499.004 technique for network denial of service attacks.
The operational impact of this vulnerability extends beyond simple application crashes, as it can be leveraged by remote attackers to disrupt services that rely on PoDoFo for PDF processing. Systems utilizing this library for document generation, conversion, or validation purposes become susceptible to denial of service conditions when handling untrusted PDF content. The vulnerability affects any application that incorporates PoDoFo 0.9.5 or earlier versions, making it particularly concerning for web applications, document processing services, and enterprise systems that handle user-uploaded PDF files. The exploitability of this vulnerability is relatively straightforward, requiring only the creation of a malformed PDF file that triggers the specific code path within the ColorChanger::GetColorFromStack function.
Mitigation strategies for CVE-2017-6840 primarily involve upgrading to a patched version of the PoDoFo library where the bounds checking has been properly implemented. Organizations should prioritize updating their systems to PoDoFo version 0.9.6 or later, which contains the necessary fixes to prevent the invalid memory read condition. Additionally, implementing proper input validation and sanitization measures at the application level can provide defense-in-depth protection against similar vulnerabilities. Security practitioners should consider deploying intrusion detection systems that can identify suspicious PDF file patterns and implementing sandboxing techniques to isolate PDF processing operations. The vulnerability also highlights the importance of regular security assessments and dependency updates to prevent exploitation of known vulnerabilities in widely-used libraries.