CVE-2021-34838 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-14019.
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Analysis
by VulDB Data Team • 08/08/2021
This vulnerability in Foxit PDF Reader version 11.0.0.49893 represents a critical remote code execution flaw that demonstrates poor input validation practices in PDF annotation processing. The vulnerability falls under CWE-476 which specifically addresses null pointer dereferences due to missing object validation. Attackers can exploit this weakness by crafting malicious PDF files containing specially constructed Annotation objects that trigger the vulnerable code path during document parsing. The flaw occurs when the application attempts to perform operations on annotation objects without first verifying their existence or proper initialization, creating a classic null pointer dereference scenario that can be leveraged for arbitrary code execution.
The operational impact of this vulnerability extends beyond simple remote code execution as it provides attackers with full control over the affected system when users interact with malicious content. Since user interaction is required through either visiting a malicious webpage or opening a crafted PDF file, this vulnerability follows the typical attack pattern described in the MITRE ATT&CK framework under technique T1203 for exploitation of remote services. The attack surface is particularly concerning given that PDF readers are commonly used for document sharing and business communications, making this vulnerability highly exploitable in enterprise environments where users frequently open PDF documents from external sources.
The technical implementation of this vulnerability stems from inadequate object validation within the PDF annotation handling subsystem of Foxit Reader. When processing annotation objects, the software fails to perform proper null checks before attempting to access object properties or methods, allowing attackers to manipulate the document structure to force the application into executing malicious code within its process context. This type of vulnerability is particularly dangerous because it operates at the application level without requiring system-level privileges, and the exploitation can occur silently in the background without user awareness. The vulnerability's classification as a remote code execution flaw means that attackers can potentially establish persistent access, escalate privileges, or deploy additional malware payloads through this initial compromise vector.
Mitigation strategies should focus on immediate patching of affected Foxit Reader installations to address the underlying validation flaw in annotation object handling. Organizations should implement network-level controls such as PDF file filtering and content inspection to prevent malicious PDF files from reaching end users. Security teams should also consider deploying application whitelisting policies that restrict execution of untrusted PDF files and implement user education programs to raise awareness about suspicious PDF attachments. Additionally, monitoring for unusual PDF processing activities and implementing sandboxing techniques for PDF document handling can provide additional layers of protection. The vulnerability's remediation aligns with standard security practices outlined in NIST SP 800-128 for vulnerability management and patch deployment, ensuring that the organization maintains a secure baseline against similar exploitation vectors.