CVE-2021-31456 in Foxit
Summary
by MITRE • 05/08/2021
This vulnerability allows remote attackers to execute arbitrary code on affected installations of Foxit Reader 10.1.1.37576. 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 Annotation objects. The issue results from the lack of validating the existence of an object prior to performing operations on the object. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-13102.
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Analysis
by VulDB Data Team • 05/04/2026
CVE-2021-31456 represents a critical remote code execution vulnerability affecting Foxit Reader version 10.1.1.37576 and potentially other versions within the 10.x release series. This vulnerability operates under the Common Weakness Enumeration framework as a weakness classified under CWE-476, specifically Null Pointer Dereference, where the software attempts to access memory locations through null pointers without proper validation. The flaw manifests in the annotation processing subsystem of the PDF reader application, which is responsible for handling various interactive elements such as comments, highlights, and form fields that users can add to PDF documents.
The technical exploitation of this vulnerability occurs when Foxit Reader processes malformed PDF files containing specially crafted annotation objects. The application fails to validate whether these annotation objects exist or are properly initialized before attempting to perform operations on them. This validation gap creates an opportunity for attackers to craft malicious PDF documents that trigger a null pointer dereference during the annotation parsing phase. When the reader attempts to access properties or methods of these uninitialized objects, the application crashes or more critically, allows for arbitrary code execution within the context of the current process, effectively elevating the attacker's privileges to match those of the Foxit Reader application itself.
The operational impact of this vulnerability extends beyond simple exploitation as it leverages the principle of user interaction required for successful attack delivery. This characteristic places the vulnerability in the ATT&CK framework under technique T1203 - Exploitation for Client Execution, where attackers must convince victims to open malicious files or visit compromised websites. The attack vector typically involves social engineering campaigns where users are lured into opening PDF documents that contain the malicious annotation objects. The vulnerability affects both Windows and macOS platforms where Foxit Reader is installed, making it particularly dangerous in enterprise environments where these applications are widely deployed.
Mitigation strategies for CVE-2021-31456 should begin with immediate patch application from Foxit Corporation, as the vendor has released security updates addressing this specific flaw. Organizations should implement network-based controls such as PDF file filtering at perimeter devices, blocking suspicious PDF content from external sources, and deploying sandboxing solutions to analyze suspicious documents before allowing user access. Additionally, security teams should consider implementing user education programs to raise awareness about phishing attempts and suspicious PDF attachments. The vulnerability's classification as a remote code execution flaw means that organizations should also review their incident response procedures to ensure rapid detection and containment of potential exploitation attempts. Network monitoring should be enhanced to detect unusual outbound connections from systems running Foxit Reader, as successful exploitation may result in command and control communications from compromised systems.