CVE-2017-16571 in Foxit
Summary
by MITRE
This vulnerability allows remote attackers to execute arbitrary code on vulnerable installations of Foxit Reader 8.3.1.21155. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file. The specific flaw exists within the handling of references to the app object from FormCalc. The issue results from the lack of proper validation of user-supplied data, which can result in a type confusion condition. An attacker can leverage this to execute code in the context of the current process. Was ZDI-CAN-5072.
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Analysis
by VulDB Data Team • 12/16/2019
CVE-2017-16571 represents a critical remote code execution vulnerability affecting Foxit Reader version 8.3.1.21155, classified under CWE-471 as "Incorrectly Handling of References to App Object from FormCalc". This vulnerability operates through a type confusion condition that arises from inadequate validation of user-supplied data within the PDF reader's FormCalc scripting environment. The flaw specifically manifests when processing references to the app object, creating a dangerous scenario where attacker-controlled data can manipulate memory structures and execute arbitrary code with the privileges of the current process.
The exploitation mechanism relies on user interaction, requiring victims to either visit a malicious webpage or open a specially crafted malicious PDF file containing the vulnerable FormCalc code. This attack vector aligns with ATT&CK technique T1203 "Exploitation for Client Execution" and demonstrates how web-based attacks can leverage PDF reader vulnerabilities to achieve remote code execution. The vulnerability's root cause stems from improper input validation and type checking within the FormCalc interpreter, which fails to properly distinguish between different data types when processing app object references, leading to memory corruption that attackers can manipulate.
The operational impact of this vulnerability extends beyond simple code execution, as it allows adversaries to gain full control over the victim's system with the privileges of the Foxit Reader process. This presents significant risk for enterprise environments where PDF readers are commonly used for document processing and collaboration. The vulnerability's classification as a type confusion issue makes it particularly dangerous because it can lead to various memory corruption scenarios including buffer overflows, use-after-free conditions, or arbitrary memory writes that can be leveraged for privilege escalation. Organizations using Foxit Reader in production environments face potential data breaches, system compromise, and lateral movement opportunities for attackers who successfully exploit this vulnerability.
Mitigation strategies should prioritize immediate patching of affected Foxit Reader installations to version 8.3.2 or later, which contains the necessary fixes for the FormCalc type confusion vulnerability. Network defenders should implement web filtering solutions to block access to known malicious PDF hosting sites and consider sandboxing PDF processing activities to limit potential damage from successful exploits. Additionally, security teams should monitor for indicators of compromise related to this vulnerability, including unusual network connections from Foxit Reader processes and unexpected code execution patterns. The vulnerability's classification under CWE-471 emphasizes the importance of proper input validation and type safety in scripting environments, making it essential for developers and security professionals to understand how to prevent similar issues in other applications that handle user-supplied data through interpreted languages or scripting interfaces.