CVE-2021-34834 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-14014.
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Analysis
by VulDB Data Team • 08/08/2021
The vulnerability identified as CVE-2021-34834 represents a critical remote code execution flaw in Foxit PDF Reader version 11.0.0.49893 that demonstrates a classic improper input validation weakness. This vulnerability falls under the CWE-476 category of NULL Pointer Dereference, where the application fails to properly validate the existence of objects 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, comments, and markup features. When a PDF document contains maliciously crafted Annotation objects, the reader's parser fails to verify whether these objects exist or are properly initialized before attempting to access their properties or methods.
The exploitation of this vulnerability requires user interaction through either visiting a malicious webpage that loads a specially crafted PDF or opening a malicious file directly, making it a typical client-side attack vector that aligns with ATT&CK technique T1203 - Exploitation for Client Execution. The root cause stems from inadequate object validation within the PDF parsing engine where the application assumes certain objects will always be present without proper null checks or existence verification. This oversight creates a pathway for attackers to craft PDF documents containing malformed Annotation objects that trigger the NULL pointer dereference when the reader attempts to process them. The execution context of the vulnerability allows attackers to run arbitrary code with the privileges of the currently running process, which typically runs with the same permissions as the user who opened the PDF document, potentially leading to full system compromise.
The operational impact of this vulnerability extends beyond simple code execution, as it represents a significant risk to enterprise environments where PDF documents are frequently shared and opened by multiple users. The vulnerability affects the core PDF rendering functionality and can be leveraged for various attack scenarios including phishing campaigns, supply chain attacks, or targeted intrusion attempts. Organizations using Foxit PDF Reader 11.0.0.49893 are particularly vulnerable as the flaw exists in the application's fundamental document parsing logic rather than in specific network services or server components. The attack surface is broad since PDF files can be transmitted through various channels including email attachments, web downloads, cloud storage services, and file sharing platforms, making this vulnerability particularly dangerous in environments with limited security controls. The vulnerability's classification as a remote code execution flaw means that attackers can potentially compromise systems without requiring physical access or additional attack vectors.
Mitigation strategies for CVE-2021-34834 should prioritize immediate patching of affected Foxit PDF Reader installations, as this represents the most effective defense against exploitation. Organizations should implement comprehensive email filtering and web proxy controls to prevent users from accessing potentially malicious PDF content, particularly when these files originate from untrusted sources. Network segmentation and application whitelisting can provide additional defense layers by restricting the execution of unauthorized PDF processing applications. Security teams should also consider deploying endpoint detection and response solutions that can monitor for suspicious PDF processing activities or unusual code execution patterns that may indicate exploitation attempts. The vulnerability's nature as a client-side flaw means that user education and awareness programs should emphasize the importance of only opening PDF files from trusted sources and avoiding suspicious email attachments or web downloads. Additionally, regular vulnerability assessments and penetration testing should include evaluation of PDF reader applications to identify similar validation flaws in other software components. Organizations should also maintain up-to-date threat intelligence feeds to monitor for exploitation attempts targeting this specific vulnerability and implement automated response procedures that can quickly isolate affected systems when exploitation is detected.