CVE-2017-7894 in WinDjView
Summary
by MITRE
WinDjView 2.1 might allow user-assisted attackers to execute code via a crafted .djvu file, because of a "User Mode Write AV near NULL" in WinDjView.exe. One threat model is a victim who obtains an untrusted .djvu file from a remote location and issues several "zoom in" (e.g., Ctrl + Plus) commands.
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Analysis
by VulDB Data Team • 07/01/2020
The vulnerability identified as CVE-2017-7894 affects WinDjView version 2.1, a popular document viewer for djvu files that is widely used in both personal and enterprise environments. This security flaw represents a critical code execution vulnerability that can be exploited through a carefully crafted malicious djvu file, demonstrating the inherent risks associated with document processing applications that handle untrusted input. The vulnerability manifests as a "User Mode Write AV near NULL" condition within the WinDjView.exe process, indicating a memory corruption issue that occurs during the application's normal operation when processing malformed input data. The specific nature of this vulnerability places it within the realm of memory safety issues that have been extensively documented in cybersecurity literature and are commonly associated with buffer overflows and access violations.
The technical exploitation of this vulnerability requires a user-assisted attack vector where an attacker must first deliver a malicious djvu file to a victim who will then interact with it using the application. The attack scenario specifically involves the victim opening the crafted file and subsequently executing multiple "zoom in" operations using keyboard shortcuts such as Ctrl + Plus, which triggers the memory corruption condition. This sequence of events aligns with common attack patterns described in the attack framework, where user interaction is required to complete the exploitation process, making it classified as a user-assisted remote code execution vulnerability. The vulnerability's classification corresponds to CWE-121, which deals with stack-based buffer overflow conditions, though the specific manifestation in this case involves heap corruption and memory access violations.
The operational impact of this vulnerability extends beyond simple code execution, as it can enable attackers to gain complete control over the victim's system. When an attacker successfully exploits this vulnerability, they can execute arbitrary code with the privileges of the user running WinDjView, potentially leading to system compromise, data theft, or further network infiltration. The vulnerability affects not only individual users but also enterprise environments where djvu files might be shared through email attachments, file servers, or web portals, making it particularly dangerous in corporate settings. The fact that the vulnerability can be triggered through normal user interactions such as zoom operations makes it especially concerning, as users may not be aware they are interacting with malicious content until after the exploit has been successfully executed. This type of vulnerability is particularly relevant in the context of zero-day exploits and advanced persistent threat campaigns where attackers leverage such flaws to establish initial access to target systems.
Mitigation strategies for CVE-2017-7894 should include immediate patching of the affected WinDjView application to the latest version that contains the necessary security fixes. Organizations should implement strict file validation policies for djvu files, particularly those received from untrusted sources, and consider deploying application whitelisting solutions to prevent execution of unauthorized software. Network-based security controls such as intrusion detection systems and web application firewalls can help detect and block attempts to deliver malicious djvu files through network channels. Additionally, user education programs should be implemented to raise awareness about the risks of opening untrusted document files and the importance of verifying file sources before processing them with document viewers. The vulnerability serves as a reminder of the importance of regular security updates and the need for robust input validation in document processing applications, aligning with security best practices outlined in frameworks such as the NIST Cybersecurity Framework and ISO 27001 standards for information security management.