CVE-2021-34839 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-14020.
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Analysis
by VulDB Data Team • 08/08/2021
The vulnerability identified as CVE-2021-34839 represents a critical remote code execution flaw in Foxit PDF Reader version 11.0.0.49893 that demonstrates a classic object validation weakness in software security architecture. 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 them. The flaw specifically manifests within the Annotation object handling mechanism, which is a fundamental component of PDF document processing that allows for interactive elements such as comments, highlights, and form fields. The vulnerability's classification aligns with ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage application vulnerabilities to execute malicious code on target systems. The attack vector requires user interaction through visiting malicious web pages or opening compromised PDF files, making it particularly dangerous in phishing campaigns and social engineering attacks.
The technical implementation of this vulnerability stems from improper input validation during PDF parsing operations, where the software does not adequately check whether Annotation objects exist before attempting to access their properties or methods. When a malicious PDF document contains crafted Annotation objects with invalid references or malformed data structures, the Foxit PDF Reader application attempts to process these objects without proper validation, leading to a situation where the software may execute arbitrary code within the context of the current process. This behavior creates a privilege escalation scenario where the malicious code runs with the same permissions as the PDF reader application, potentially allowing attackers to access system resources, modify files, or establish persistence mechanisms. The vulnerability's exploitation pathway demonstrates a common pattern in PDF reader security flaws where insufficient validation of document elements leads to memory corruption and arbitrary code execution.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a potential foothold for more sophisticated attacks within target environments. Since the vulnerability requires user interaction, it typically manifests through phishing emails containing malicious PDF attachments or compromised websites hosting malicious content, making it particularly challenging to defend against through network-level controls alone. Organizations using Foxit PDF Reader in enterprise environments face significant risk exposure, as the vulnerability could be exploited to bypass traditional security controls and gain unauthorized access to sensitive documents and system resources. The attack complexity is moderate, requiring the creation of a malicious PDF file that specifically targets the Annotation object handling code path, but the potential impact is severe enough to warrant immediate remediation efforts. The vulnerability's presence in a widely-used PDF reader application means that successful exploitation could compromise numerous endpoints across different organizations, particularly those that do not maintain strict software update policies.
Mitigation strategies for CVE-2021-34839 should focus on immediate patch management and operational security enhancements. Organizations must prioritize updating Foxit PDF Reader installations to versions that address this vulnerability, as the manufacturer has released patches to correct the object validation issues in Annotation handling. Network administrators should implement additional security measures such as PDF file scanning, web filtering, and email attachment restrictions to reduce the likelihood of users encountering malicious PDF content. The vulnerability's characteristics make it particularly suitable for targeted attacks, so security teams should monitor for suspicious PDF-related activities and implement behavioral analysis tools that can detect anomalous processing patterns. Regular security assessments of PDF processing applications should include specific testing of object validation mechanisms, and organizations should consider implementing sandboxing technologies to isolate PDF processing activities from core system resources. Incident response plans should be updated to include procedures for handling PDF-based attacks, and security awareness training should emphasize the dangers of opening unexpected PDF files from untrusted sources. The vulnerability's remediation also highlights the importance of following secure coding practices such as input validation, proper error handling, and defensive programming techniques that prevent similar flaws from occurring in future software versions.