CVE-2021-34840 in Foxit
Summary
by MITRE • 08/04/2021
This vulnerability allows remote attackers to execute arbitrary code on affected installations of Foxit PDF Reader 11.0.0.49893. 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-14021.
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Analysis
by VulDB Data Team • 08/08/2021
The vulnerability identified as CVE-2021-34840 represents a critical remote code execution flaw in Foxit PDF Reader version 11.0.0.49893, demonstrating a classic improper input validation issue that has significant implications for document security. This vulnerability falls under the CWE-476 category of NULL Pointer Dereference, where the application fails to properly validate object existence before attempting operations on it. The flaw specifically manifests within the Annotation object handling mechanism, which is a fundamental component of PDF documents used for adding notes, comments, and interactive elements to documents.
The technical exploitation of this vulnerability requires user interaction through either visiting a malicious webpage or opening a specially crafted PDF file containing malformed Annotation objects. This attack vector aligns with ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage application vulnerabilities to execute malicious code on target systems. The root cause lies in the absence of proper validation checks that should occur before object operations, allowing an attacker to construct malicious PDF content that triggers the vulnerability when processed by the vulnerable reader application.
When the vulnerable Foxit PDF Reader processes a malicious Annotation object, the application attempts to perform operations on what it believes to be a valid object but which may not exist or may be improperly structured. This creates a condition where the application's memory management becomes compromised, enabling an attacker to inject and execute arbitrary code within the context of the running process. The exploitation occurs at the application level, meaning the malicious code executes with the privileges of the user running Foxit PDF Reader, potentially leading to full system compromise if the user has administrative privileges.
The operational impact of this vulnerability extends beyond simple code execution, as it represents a sophisticated attack surface that could be leveraged for more advanced persistent threats. Security researchers have noted that PDF readers represent high-value targets due to their widespread use and the trust users place in document processing applications. The vulnerability's classification as a remote code execution flaw means that attackers can compromise systems without physical access, making it particularly dangerous in enterprise environments where PDF documents are frequently shared and opened. Organizations using Foxit PDF Reader version 11.0.0.49893 face significant risk of unauthorized code execution, data exfiltration, and potential lateral movement within their networks.
Mitigation strategies for CVE-2021-34840 should prioritize immediate patching of affected Foxit PDF Reader installations to version 11.0.1.49900 or later, which contains the necessary fixes for the Annotation object validation issues. System administrators should implement network-based controls to monitor and restrict access to potentially malicious PDF content, particularly in environments where users frequently encounter untrusted documents. Additionally, organizations should consider deploying sandboxing solutions for PDF processing and implementing user education programs to reduce the risk of successful exploitation through social engineering attacks. The vulnerability demonstrates the critical importance of input validation in document processing applications and serves as a reminder of the need for comprehensive security testing in software that handles user-provided content, particularly in environments where such content may be inherently untrusted.