CVE-2018-3956 in Foxit
Summary
by MITRE
An exploitable out-of-bounds read vulnerability exists in the handling of certain XFA element attributes of Foxit Software's PDF Reader version 9.1.0.5096. A specially crafted PDF document can trigger an out-of-bounds read, which can disclose sensitive memory content and aid in exploitation when coupled with another vulnerability. 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 • 07/04/2023
The vulnerability identified as CVE-2018-3956 represents a critical out-of-bounds read flaw within Foxit Software's PDF Reader application version 9.1.0.5096, specifically affecting the processing of XFA element attributes. This type of vulnerability falls under the common weakness enumeration CWE-125 which describes out-of-bounds read conditions where programs access memory locations beyond the intended buffer boundaries. The flaw manifests when the PDF reader encounters specially crafted XFA (XML Forms Architecture) elements within malicious PDF documents, creating a scenario where memory access occurs beyond the allocated buffer limits. The vulnerability is particularly concerning as it can potentially expose sensitive memory content to attackers, providing them with valuable information that could aid in developing more sophisticated exploitation techniques. The security implications extend beyond simple information disclosure, as this vulnerability can serve as a stepping stone for attackers to combine with other vulnerabilities to achieve more severe outcomes such as arbitrary code execution or privilege escalation.
The technical exploitation of this vulnerability requires a user interaction component where an attacker must convince the victim to open a maliciously crafted PDF file. This social engineering aspect is crucial as it demonstrates the practical attack vector that makes this vulnerability exploitable in real-world scenarios. The attack can be delivered through traditional means such as email attachments or malicious file downloads, but also through web-based delivery methods when the browser plugin extension is enabled. When the browser plugin is active, visiting a malicious website can trigger the vulnerability without requiring the user to download a file, expanding the attack surface significantly. This dual delivery mechanism makes the vulnerability particularly dangerous as it can be exploited through multiple vectors, increasing the likelihood of successful compromise. The XFA element processing within the PDF reader appears to lack proper bounds checking when handling attribute values, allowing attackers to manipulate the parsing process and force memory access beyond valid boundaries.
The operational impact of CVE-2018-3956 extends beyond immediate information disclosure to potentially enable more sophisticated attack chains. When combined with other vulnerabilities present in the same system or application, this out-of-bounds read can facilitate advanced exploitation techniques such as information leakage attacks that help attackers understand memory layouts, or can be used to bypass security mechanisms like address space layout randomization. The vulnerability affects a widely used PDF reader application, meaning that organizations and individuals who rely on Foxit Reader for document processing are at risk. The exploitation requires minimal privileges and can be executed remotely, making it particularly attractive to threat actors seeking to compromise endpoints. Security researchers have noted that such vulnerabilities often remain undetected for extended periods, as they may not immediately manifest in obvious ways during normal usage, allowing attackers to develop and deploy exploits without immediate detection.
Mitigation strategies for this vulnerability should focus on both immediate remediation and long-term security hardening measures. The most effective immediate solution is to update to a patched version of Foxit PDF Reader, as the vendor would have addressed the bounds checking deficiencies in the XFA element processing code. Organizations should implement strict document filtering policies that prevent the opening of PDF files from untrusted sources, particularly when these files are received through email or web-based channels. Network-level controls can be implemented to block potentially malicious PDF content at the perimeter, reducing the risk of successful exploitation. Additionally, browser security configurations should be reviewed to ensure that plugin extensions are properly managed, with unnecessary plugins disabled to minimize attack surface. The vulnerability highlights the importance of input validation and bounds checking in security-critical applications, particularly those handling untrusted data formats like PDF documents. Security monitoring should be enhanced to detect unusual memory access patterns or attempts to access restricted memory regions that might indicate exploitation attempts. Regular security assessments of document processing applications are recommended to identify similar vulnerabilities in other software components that handle complex data formats. The vulnerability serves as a reminder of the ongoing need for robust software security practices and the critical importance of timely patch management in maintaining secure computing environments.