CVE-2021-34843 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-14025.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 08/08/2021
The vulnerability identified as CVE-2021-34843 represents a critical remote code execution flaw in Foxit PDF Reader version 11.0.0.49893 that demonstrates a classic object validation error pattern commonly found in software applications handling complex file formats. This vulnerability operates under the weakness category defined by 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 annotation 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 an attacker to craft a malicious PDF file containing specially constructed annotation objects that trigger the validation gap during processing. When a user visits a malicious webpage hosting such a PDF file or directly opens the crafted document, the PDF reader's annotation handling code path is triggered. The application attempts to perform operations on what it believes to be a valid annotation object, but due to the missing validation check, it processes a null or invalid reference, leading to memory corruption that can be controlled to execute arbitrary code. This type of vulnerability aligns with ATT&CK technique T1203 which describes exploitation of software vulnerabilities through manipulation of input data to achieve code execution in the context of the target application process.
The operational impact of this vulnerability extends beyond simple remote code execution as it provides attackers with full control over the affected system where Foxit PDF Reader is installed. Since the exploitation occurs within the context of the PDF reader process, attackers can potentially escalate privileges, access sensitive system files, and establish persistent access through the compromised application. The requirement for user interaction through visiting malicious web pages or opening malicious files makes this vulnerability particularly dangerous in targeted attack scenarios where social engineering can be employed to deliver the malicious content. This vulnerability represents a significant risk to organizations where PDF documents are frequently opened, as it can be exploited through various attack vectors including email attachments, web-based document sharing, and malicious websites.
Mitigation strategies for CVE-2021-34843 should focus on immediate patching of the affected Foxit PDF Reader version, while also implementing network-based controls to block access to known malicious PDF content. Organizations should consider deploying web application firewalls and content filtering solutions that can detect and block suspicious PDF files before they reach end users. Additionally, user education regarding the dangers of opening unknown PDF files and visiting untrusted websites remains crucial in preventing exploitation. The vulnerability demonstrates the importance of proper input validation and object existence checking in software development practices, particularly for applications that process complex file formats where malformed input can lead to severe security consequences. Security teams should also monitor for any related vulnerabilities in similar PDF processing libraries and ensure comprehensive testing of input validation mechanisms in all file processing components.