CVE-2021-38566 in Foxit
Summary
by MITRE • 08/12/2021
An issue was discovered in Foxit PDF Reader before 11.0.1 and PDF Editor before 11.0.1. It allows stack consumption during recursive processing of embedded XML nodes.
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Analysis
by VulDB Data Team • 08/16/2021
The vulnerability identified as CVE-2021-38566 represents a critical stack consumption issue affecting Foxit PDF Reader and PDF Editor versions prior to 11.0.1. This flaw manifests during the recursive processing of embedded xml nodes within pdf documents, creating a condition where the application's call stack progressively consumes memory resources without proper bounds checking. The vulnerability falls under the category of excessive resource consumption, specifically targeting stack memory allocation patterns that occur when parsing nested xml structures. According to cwe-400, this issue is classified as an insufficient resource pool sizing, where the application fails to properly manage memory allocation limits during recursive operations. The flaw is particularly concerning because it can be exploited through crafted pdf documents containing deeply nested xml elements, allowing attackers to trigger a stack overflow condition that may lead to application instability or potential code execution.
The technical implementation of this vulnerability involves the recursive parsing mechanism used by Foxit's pdf processing engine when encountering embedded xml content within pdf files. When a pdf document contains xml nodes that are deeply nested or contain circular references, the recursive processing function calls continue to consume stack space without adequate termination conditions or stack depth limits. This recursive processing pattern is commonly used for parsing structured data within pdf documents, but the lack of proper stack management creates an exploitable condition. The vulnerability is categorized under attack technique T1203 in the ATT&CK framework as it represents a resource exhaustion attack vector that can lead to denial of service conditions. The flaw demonstrates poor input validation and insufficient bounds checking during xml parsing operations, which are fundamental security practices that should prevent unbounded recursive calls from consuming excessive system resources.
The operational impact of CVE-2021-38566 extends beyond simple denial of service scenarios, as it can potentially enable more sophisticated attacks depending on the execution environment. When exploited successfully, this vulnerability can cause pdf reader applications to crash or become unresponsive, effectively preventing legitimate users from accessing pdf documents. The stack consumption behavior can be amplified through carefully crafted malicious pdf files that contain deeply nested xml structures designed to maximize stack allocation. Organizations relying on Foxit products for document processing and viewing are particularly vulnerable to this issue, as it can be triggered through normal pdf document handling without requiring special privileges or complex attack vectors. The vulnerability affects both pdf reader and editor functionalities, meaning that any pdf document processing workflow using affected versions could be compromised. According to industry best practices for secure coding, this type of vulnerability should be prevented through proper stack depth monitoring, recursive call limiting, and input validation mechanisms that prevent unbounded processing.
Mitigation strategies for CVE-2021-38566 should prioritize immediate patching of affected Foxit products to version 11.0.1 or later, which contains the necessary fixes for proper stack management during xml processing. Organizations should implement additional protective measures including pdf document sanitization processes that remove or sanitize embedded xml content before processing, network-based filtering that blocks suspicious pdf files, and application whitelisting to restrict execution of untrusted pdf documents. Security teams should monitor for exploitation attempts through network traffic analysis and endpoint detection systems that can identify abnormal stack consumption patterns. The fix implemented by Foxit likely includes stack depth limiting mechanisms, recursive call termination conditions, and enhanced input validation for xml parsing operations. Organizations should also consider implementing sandboxing techniques for pdf processing to isolate potential exploitation attempts from critical system resources. Regular security assessments and vulnerability scanning should be conducted to ensure that similar issues are not present in other pdf processing components or related software systems. The vulnerability serves as a reminder of the importance of proper memory management in recursive algorithms and the necessity of implementing defensive programming practices to prevent resource exhaustion attacks.