CVE-2018-3939 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 • 04/29/2023
The vulnerability identified as CVE-2018-3939 represents a critical use-after-free flaw within the JavaScript engine of Foxit PDF Reader version 9.1.0.5096, classified under CWE-416 which specifically addresses use of freed memory conditions. This vulnerability exists in the context of PDF document processing where the JavaScript engine fails to properly manage object lifecycles, creating opportunities for memory corruption attacks. The flaw manifests when a malicious PDF document is processed by the reader, causing previously deallocated memory objects to be accessed again, which can lead to unpredictable behavior and potential code execution. The vulnerability's exploitation requires user interaction through opening a malicious file or visiting a compromised website when the browser plugin extension is enabled, making it particularly concerning for web-based attack vectors.
The technical implementation of this vulnerability involves memory management failures within the JavaScript engine's garbage collection and object lifecycle management mechanisms. When processing malicious PDF content, the engine allocates memory for JavaScript objects and subsequently frees them when no longer referenced. However, the flaw allows for scenarios where references to these freed objects remain in the system, enabling attackers to manipulate memory contents through controlled input data. This type of vulnerability is particularly dangerous because it can be triggered through multiple vectors including direct file execution and web-based attacks, expanding the attack surface significantly. The use-after-free condition creates a scenario where attackers can overwrite freed memory locations with malicious data, potentially leading to arbitrary code execution with the privileges of the compromised application.
The operational impact of CVE-2018-3939 extends beyond simple privilege escalation as it represents a complete compromise of the affected system's security posture. When successfully exploited, the vulnerability allows attackers to execute arbitrary code within the context of the PDF reader application, potentially leading to full system compromise. The attack vector through browser plugins makes this vulnerability particularly dangerous for enterprise environments where users frequently browse the internet and interact with PDF documents. The vulnerability's exploitation can result in data theft, system persistence mechanisms, lateral movement within networks, and the installation of additional malware. Organizations using Foxit PDF Reader in their workflows face significant risk exposure, particularly in environments where users have administrative privileges or access to sensitive information.
Mitigation strategies for CVE-2018-3939 should focus on immediate remediation through software updates and patches provided by Foxit Software, as well as implementing defensive measures to limit exposure. The primary recommendation involves updating to the latest version of Foxit PDF Reader that contains fixes for this vulnerability, which should address the underlying memory management issues in the JavaScript engine. Organizations should also consider implementing application whitelisting policies that restrict the execution of PDF readers from untrusted sources, and deploy network-based protections such as web application firewalls to block malicious PDF content. Additionally, user education regarding the dangers of opening suspicious PDF files and visiting untrusted websites remains critical. Security professionals should monitor for exploitation attempts through network traffic analysis and endpoint detection systems, as the vulnerability's exploitation typically manifests through specific memory access patterns that can be detected by security monitoring tools. The ATT&CK framework categorizes this vulnerability under T1059 for command and scripting interpreter and T1078 for valid accounts, indicating the potential for privilege escalation and persistent access once the initial exploitation succeeds.