CVE-2019-14293 in Xpdf
Summary
by MITRE
An issue was discovered in Xpdf 4.01.01. There is an out of bounds read in the function GfxPatchMeshShading::parse at GfxState.cc for typeA!=6 case 2.
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Analysis
by VulDB Data Team • 11/13/2023
The vulnerability identified as CVE-2019-14293 resides within the Xpdf 4.01.01 document rendering library, specifically within the GfxPatchMeshShading::parse function located in the GfxState.cc source file. This issue represents a critical out-of-bounds read condition that occurs when processing PDF documents containing specific shading patterns. The flaw manifests specifically during the parsing of patch mesh shading data where the typeA parameter does not equal six, and more precisely in case two of the conditional logic. Such vulnerabilities in PDF rendering engines pose significant security risks as they can be exploited through maliciously crafted PDF files that leverage the specific shading pattern structures to trigger the out-of-bounds memory access.
The technical nature of this vulnerability stems from insufficient input validation and boundary checking within the patch mesh shading parsing logic. When the GfxPatchMeshShading::parse function encounters a patch mesh shading object with typeA!=6 and case 2, it fails to properly validate array indices or memory boundaries before accessing memory locations. This allows an attacker to craft a PDF document with malformed patch mesh shading data that causes the application to read memory beyond the allocated buffer boundaries. The out-of-bounds read can potentially expose sensitive memory contents, contribute to information disclosure, and may serve as a precursor for more severe exploitation techniques such as remote code execution. This vulnerability directly maps to CWE-125, which describes out-of-bounds read conditions in software implementations, and aligns with ATT&CK technique T1059.007 for execution through document files.
The operational impact of this vulnerability extends beyond simple information disclosure, as it represents a potential entry point for more sophisticated attacks. When a victim opens a malicious PDF file containing the crafted patch mesh shading data, the application crashes or behaves unpredictably due to the memory access violation. However, the true danger lies in the potential for exploitation through memory corruption that could be leveraged to achieve arbitrary code execution. Security researchers have noted that PDF rendering engines like Xpdf are frequently targeted in phishing campaigns and exploit kits because they are commonly used components in email clients, web browsers, and document viewers. The vulnerability affects systems running Xpdf 4.01.01 and potentially earlier versions, making it particularly concerning for organizations that have not yet updated their PDF processing components.
Mitigation strategies for CVE-2019-14293 should prioritize immediate patching of the Xpdf library to the latest available version that contains the fix for this out-of-bounds read condition. Organizations should implement defensive measures such as PDF sandboxing, content filtering, and restricted file type handling to minimize exposure to malicious PDF documents. Network-level protections including web application firewalls and email filtering systems can help detect and block suspicious PDF content before it reaches end-user systems. Additionally, regular security assessments of PDF processing components, including vulnerability scanning and penetration testing, should be conducted to identify similar issues in other document rendering libraries. The fix for this vulnerability typically involves implementing proper boundary checks and input validation within the GfxPatchMeshShading::parse function, ensuring that array indices and memory access operations are properly validated before execution. Security teams should also consider implementing user awareness training to reduce the risk of social engineering attacks that might deliver malicious PDF files containing this vulnerability.