CVE-2021-34841 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-14022.
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Analysis
by VulDB Data Team • 08/08/2021
CVE-2021-34841 represents a critical remote code execution vulnerability affecting Foxit PDF Reader version 11.0.0.49893 that demonstrates a classic improper input validation flaw categorized under CWE-476. This vulnerability stems from insufficient validation of Annotation objects within the PDF parsing mechanism, where the application fails to verify the existence of objects before attempting operations on them. The flaw exists in the PDF reader's object handling subsystem and manifests when processing maliciously crafted PDF files containing malformed Annotation objects. Attackers can exploit this weakness by crafting malicious PDF documents that contain specially constructed Annotation objects designed to trigger the validation bypass, leading to arbitrary code execution in the context of the current process. The vulnerability requires user interaction to be exploited, as victims must either visit a malicious webpage hosting the exploit or open a malicious PDF file, making it particularly dangerous in phishing campaigns and drive-by download attacks.
The technical implementation of this vulnerability follows established patterns seen in memory corruption exploits and demonstrates characteristics consistent with the attack technique described in MITRE ATT&CK framework under T1203 - Exploitation for Client Execution. The flaw essentially creates a use-after-free condition or null pointer dereference scenario where the PDF reader attempts to access memory locations that have either been freed or were never properly initialized. When processing Annotation objects, the application's parser does not perform adequate bounds checking or object existence validation before invoking methods or accessing properties of these objects. This allows an attacker to manipulate the PDF structure to cause the application to execute unintended code paths, potentially leading to full system compromise. The vulnerability's impact is particularly severe because PDF readers operate with high privileges and often have extensive access to system resources, file systems, and network capabilities.
The operational impact of CVE-2021-34841 extends beyond simple code execution, as it represents a significant threat vector for advanced persistent threats and targeted attacks. Attackers leveraging this vulnerability can potentially establish persistent backdoors, escalate privileges, or exfiltrate sensitive data from compromised systems. The vulnerability affects a widely deployed PDF reader application, increasing its attack surface significantly since Foxit PDF Reader is used across enterprise environments, government agencies, and individual users. The fact that exploitation requires user interaction does not diminish the threat level, as social engineering campaigns can effectively target unsuspecting users through email attachments, malicious websites, or compromised web applications. Security researchers have noted that this vulnerability is particularly dangerous in enterprise environments where PDF files are frequently exchanged and where users may not be adequately trained to identify malicious content.
Mitigation strategies for CVE-2021-34841 should encompass both immediate defensive measures and long-term architectural improvements. Organizations should prioritize applying vendor patches and updates as soon as they become available, as Foxit likely released a fix for this vulnerability in their subsequent releases. Network administrators should implement content filtering solutions that can detect and block malicious PDF files, particularly those containing suspicious Annotation objects or unusual file structures. Additionally, implementing application whitelisting policies and restricting PDF reader execution from untrusted sources can significantly reduce the attack surface. Users should be educated about the risks of opening PDF files from unknown sources and trained to recognize potential phishing attempts. Security teams should also consider deploying sandboxing solutions that can isolate PDF processing in isolated environments, preventing malicious code from affecting the primary system. The vulnerability highlights the importance of robust input validation and proper object lifecycle management in PDF processing libraries, emphasizing the need for security-by-design principles in document handling applications.