CVE-2020-26537 in Foxit
Summary
by MITRE • 10/04/2020
An issue was discovered in Foxit Reader and PhantomPDF before 10.1. In a certain Shading calculation, the number of outputs is unequal to the number of color components in a color space. This causes an out-of-bounds write.
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Analysis
by VulDB Data Team • 11/15/2020
The vulnerability identified as CVE-2020-26537 represents a critical memory safety issue affecting Foxit Reader and PhantomPDF versions prior to 10.1. This flaw manifests within the shading calculation functionality of these PDF processing applications, where improper handling of color space components leads to memory corruption. The issue stems from a fundamental mismatch between expected and actual data quantities during the rendering process, creating conditions that allow attackers to execute arbitrary code through maliciously crafted PDF documents. The vulnerability specifically targets the color space handling mechanisms within PDF shading objects, which are used to create complex visual effects and gradients in documents.
The technical root cause of this vulnerability lies in an out-of-bounds write condition that occurs when the application processes shading calculations with color spaces containing an unequal number of outputs compared to color components. This discrepancy creates a situation where the application attempts to write data beyond the allocated memory boundaries for color component arrays. According to CWE classification, this vulnerability maps to CWE-787: "Out-of-bounds Write," which is a direct consequence of inadequate input validation and memory management in the PDF rendering engine. The flaw demonstrates characteristics of CWE-129: "Improper Validation of Array Index," as the application fails to properly validate the relationship between color component counts and output values during shading operations.
The operational impact of CVE-2020-26537 extends beyond simple document rendering issues, as it provides a potential attack vector for remote code execution. When a user opens a malicious PDF document containing specially crafted shading objects, the application's failure to properly validate color space parameters triggers the out-of-bounds write condition. This memory corruption can be leveraged by attackers to overwrite critical memory locations, potentially leading to arbitrary code execution with the privileges of the affected application. The vulnerability is particularly concerning in enterprise environments where users frequently open PDF documents from untrusted sources, making it a prime target for phishing campaigns and targeted attacks. The ATT&CK framework categorizes this vulnerability under T1203: "Exploitation for Client Execution" as it exploits application vulnerabilities to execute malicious code on target systems.
Mitigation strategies for CVE-2020-26537 primarily focus on immediate application updates and security hardening measures. Organizations should prioritize updating to Foxit Reader version 10.1 or later, which includes patches addressing the color space validation issues. Additionally, implementing PDF sandboxing mechanisms and restricting PDF document handling to trusted sources can significantly reduce the risk exposure. Network-level protections such as PDF content filtering and web application firewalls can provide additional defense-in-depth measures. Security teams should also consider implementing behavioral monitoring to detect anomalous shading calculation patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper input validation and memory safety practices in PDF rendering engines, aligning with industry best practices for secure software development and the recommendations outlined in the OWASP Top Ten and NIST Cybersecurity Framework.