CVE-2019-20828 in Foxit
Summary
by MITRE
An issue was discovered in Foxit Reader and PhantomPDF before 9.6. It has a buffer overflow because a looping correction does not occur after JavaScript updates Field APs.
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Analysis
by VulDB Data Team • 10/22/2020
The vulnerability identified as CVE-2019-20828 represents a critical buffer overflow flaw affecting Foxit Reader and PhantomPDF versions prior to 9.6. This security issue stems from improper handling of JavaScript updates within PDF documents, specifically concerning the manipulation of field appearance dictionaries. The flaw occurs when JavaScript code attempts to modify the appearance properties of form fields, creating a scenario where iterative corrections fail to properly validate buffer boundaries. This particular vulnerability falls under the CWE-121 category of stack-based buffer overflow, though it manifests in a more complex manner due to the dynamic nature of JavaScript execution within PDF environments. The issue demonstrates how interactive PDF features can become attack vectors when proper input validation and boundary checking mechanisms are absent during field property modifications.
The technical exploitation of this vulnerability occurs through maliciously crafted PDF documents that contain JavaScript code designed to repeatedly update form field appearance properties. When the vulnerable software processes these updates, the looping correction mechanism fails to properly manage memory allocation for the appearance dictionaries, leading to buffer overflow conditions. This allows attackers to potentially overwrite adjacent memory locations, which could result in arbitrary code execution or application crashes. The flaw is particularly dangerous because it leverages the legitimate JavaScript functionality that PDF readers support, making it difficult to distinguish between benign and malicious code execution. The vulnerability demonstrates a classic example of how dynamic content manipulation in document processing software can create memory safety issues when proper bounds checking is not implemented.
The operational impact of CVE-2019-20828 extends beyond simple application instability, as it provides potential attackers with pathways for remote code execution within the context of the PDF reader. Organizations using affected versions of Foxit Reader or PhantomPDF face significant risks when processing untrusted PDF documents, particularly in environments where users may encounter maliciously crafted files through email attachments, web downloads, or document sharing platforms. The vulnerability affects the core document rendering functionality and could be exploited in targeted attacks against specific user groups, such as legal professionals or financial institutions who frequently handle sensitive documents containing form fields. Security researchers have noted that this vulnerability aligns with ATT&CK technique T1059.007 for JavaScript execution, where adversaries leverage legitimate software features to execute malicious code. The attack surface is particularly concerning given that PDF readers are commonly used across multiple operating systems and environments, amplifying the potential impact of successful exploitation.
Organizations should prioritize immediate remediation by upgrading to Foxit Reader version 9.6 or later, which includes proper bounds checking and correction mechanisms for field appearance updates. System administrators should implement strict PDF document filtering policies and consider deploying sandboxing solutions to isolate PDF processing activities. The mitigation strategy should also include regular security awareness training for users to recognize potentially malicious PDF attachments and implement network-level controls to prevent unauthorized PDF document downloads. Additionally, organizations should conduct vulnerability assessments to identify any systems running older versions of the software and establish patch management procedures to ensure timely updates. Security monitoring should include detection of suspicious JavaScript activity within PDF documents, particularly when form fields are being manipulated, as this represents a key indicator of potential exploitation attempts. The vulnerability serves as a reminder of the importance of memory safety in document processing applications and the need for comprehensive input validation mechanisms in dynamic content environments.