CVE-2021-34835 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-14015.
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Analysis
by VulDB Data Team • 08/08/2021
CVE-2021-34835 represents a critical remote code execution vulnerability affecting Foxit PDF Reader version 11.0.0.49893 and potentially other versions within the 11.0.0.x series. This vulnerability falls under the Common Weakness Enumeration category CWE-476 which specifically addresses NULL pointer dereferences and improper handling of null object references. The flaw manifests in the PDF reader's annotation processing module where the software fails to validate whether an object exists before attempting operations on it. This fundamental validation gap creates a dangerous condition where maliciously crafted PDF files can trigger unexpected behavior in the application's memory management.
The exploitation mechanism requires user interaction through either visiting a malicious webpage that loads a crafted PDF or opening a specially constructed PDF file directly. This interaction model aligns with the ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage vulnerabilities in software applications to execute malicious code. When a user opens the malicious document, the PDF reader's annotation handler processes the malformed object without proper validation, leading to a situation where the application attempts to dereference a null pointer or access invalid memory locations. This memory corruption allows attackers to inject and execute arbitrary code within the context of the Foxit PDF Reader process, potentially with the privileges of the user running the application.
The operational impact of this vulnerability extends beyond simple code execution as it provides attackers with a persistent foothold within the victim's system. Since the vulnerability operates at the application level and does not require administrative privileges to exploit, it can be leveraged for various malicious activities including data exfiltration, privilege escalation, or as a staging point for additional attacks. The fact that this vulnerability exists in a widely used PDF reader application means it could be exploited at scale through phishing campaigns or compromised websites. The attack surface is particularly concerning given that PDF files are commonly shared through email, web downloads, and document management systems, making this a high-risk vulnerability for organizations and individual users alike.
Organizations should implement immediate mitigations including updating to the latest version of Foxit PDF Reader where the vulnerability has been patched, disabling PDF handling in web browsers where possible, and implementing strict email filtering and web content security policies. Network-based protections such as web application firewalls and intrusion detection systems can help detect and block exploitation attempts. Additionally, user education regarding the dangers of opening untrusted PDF files and the importance of keeping software updated remains crucial. The vulnerability demonstrates the importance of proper input validation and object lifecycle management in software development, particularly in applications that process untrusted data from external sources. This case study reinforces the necessity of following secure coding practices and conducting thorough security testing, especially for applications handling complex file formats like PDF documents that require extensive parsing and object manipulation.