CVE-2021-34833 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-14023.
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Analysis
by VulDB Data Team • 08/08/2021
The vulnerability identified as CVE-2021-34833 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 operates under the Common Weakness Enumeration framework as CWE-476, which specifically addresses NULL pointer dereferences and improper object validation scenarios. The flaw manifests within the PDF reader's annotation processing subsystem where the application fails to properly validate whether referenced objects exist before attempting to perform operations on them, creating an exploitable condition that can be leveraged by remote attackers.
The technical exploitation of this vulnerability requires a user to interact with malicious content, typically through visiting a specially crafted web page or opening a malicious PDF file that contains crafted annotation objects. This user interaction requirement aligns with the ATT&CK framework's technique T1203, which describes social engineering tactics used to gain initial access to systems. The vulnerability's root cause lies in the improper object lifecycle management within the PDF parsing engine, where annotation objects are processed without adequate validation checks that would normally occur before object manipulation. When the application attempts to access a non-existent object reference, it triggers a memory corruption condition that can be exploited to inject and execute arbitrary code within the context of the running PDF reader process.
The operational impact of this vulnerability extends beyond simple remote code execution to encompass potential full system compromise, as the exploitation occurs within the privileges of the currently running user account. The vulnerability affects the integrity of the PDF reader's sandboxing mechanisms, potentially allowing attackers to bypass security controls designed to isolate PDF processing from the underlying operating system. This represents a significant risk to enterprise environments where PDF readers are frequently used for document processing, as it could enable attackers to establish persistent access through the exploitation of trusted applications. The vulnerability's exploitation requires minimal user interaction beyond normal document opening behavior, making it particularly dangerous in targeted attack scenarios.
Organizations should implement immediate mitigations including updating to the latest version of Foxit PDF Reader where the vulnerability has been patched, disabling PDF reader integration in web browsers, and implementing network-level controls to block access to known malicious domains. Security teams should also consider deploying endpoint detection and response solutions that can monitor for suspicious process behavior and memory access patterns associated with this type of exploitation. The vulnerability demonstrates the critical importance of input validation and object lifecycle management in security-critical applications, serving as a reminder that even seemingly simple validation checks can prevent sophisticated exploitation techniques. Organizations should also review their incident response procedures to ensure readiness for potential exploitation of similar vulnerabilities in other PDF processing applications.