CVE-2018-3943 in Foxit
Summary
by MITRE
An exploitable use-after-free vulnerability exists in the JavaScript engine of Foxit Software's PDF Reader, version 9.1.0.5096. A specially crafted PDF document can trigger a previously freed object in memory to be reused, resulting in arbitrary code execution. An attacker needs to trick the user to open the malicious file to trigger this vulnerability. If the browser plugin extension is enabled, visiting a malicious site can also trigger the vulnerability.
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Analysis
by VulDB Data Team • 07/30/2024
The vulnerability identified as CVE-2018-3943 represents a critical use-after-free flaw within the JavaScript engine of Foxit PDF Reader version 9.1.0.5096, classified under CWE-416 as use of freed memory. This type of vulnerability occurs when a program continues to reference memory that has already been freed, creating opportunities for attackers to manipulate the program's execution flow. The flaw specifically affects the JavaScript engine's memory management system where objects are not properly validated before reuse, creating a potential pathway for arbitrary code execution. The vulnerability is particularly dangerous because it can be triggered through multiple attack vectors including direct file opening and web-based exploitation when browser plugin extensions are enabled.
The technical exploitation of this vulnerability requires an attacker to craft a malicious PDF document that forces the JavaScript engine to access memory that has already been deallocated. When the PDF reader processes such a document, the JavaScript engine attempts to access a freed object in memory, potentially allowing an attacker to inject and execute malicious code with the privileges of the user running the application. This use-after-free condition typically arises from inadequate null pointer checks or improper reference counting mechanisms within the JavaScript engine's memory management subsystem. The vulnerability demonstrates a classic memory safety issue where the program fails to maintain proper object lifecycle management, allowing freed memory to be accessed and manipulated by malicious code.
The operational impact of CVE-2018-3943 extends beyond simple code execution to encompass potential full system compromise, as the JavaScript engine in PDF readers often operates with elevated privileges when processing embedded scripts. Attackers can leverage this vulnerability to bypass security controls, escalate privileges, or establish persistent access to target systems. The attack surface is particularly broad since PDF readers are commonly used across multiple platforms and are often automatically launched when users open PDF files from email attachments or web downloads. When browser plugin extensions are enabled, the vulnerability can be triggered through web navigation, expanding the attack surface to include web-based delivery methods and potentially affecting users who may not be directly targeted by malicious file attachments.
Mitigation strategies for this vulnerability should focus on immediate patching of the Foxit PDF Reader software to version 9.1.1.5102 or later, which contains the necessary memory management fixes. Organizations should implement strict email filtering and web access controls to prevent users from inadvertently opening malicious PDF files. Network-based protections such as web proxies with PDF content filtering can help detect and block suspicious PDF documents before they reach end users. Additionally, users should be trained to avoid opening PDF files from untrusted sources and to disable JavaScript execution in PDF readers when not required for legitimate business functions. The vulnerability highlights the importance of regular software updates and proper input validation in preventing memory safety issues, aligning with ATT&CK technique T1059.007 for JavaScript and T1203 for exploitation for execution through web-based attacks.