CVE-2026-91793 in PDF Editor
Summary
by MITRE • 09/23/2026
When opening a specially crafted PDF, Foxit PDF Editor/Reader executes scripts that modify annotation rich-text attributes containing malformed font data. During subsequent annotation appearance reconstruction, it accesses an object after it has been released, resulting in a use-after-free condition and an application crash.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified involves a critical memory management flaw within Foxit PDF Editor and Reader, specifically triggered by the processing of maliciously crafted Portable Document Format files. The attack vector centers on the execution of embedded scripts that manipulate annotation rich-text attributes. These annotations are designed to contain malformed font data structures that deviate from expected formatting standards. When the application parses these specific elements during document rendering or interaction, it initiates a sequence of operations aimed at reconstructing the visual appearance of the annotated content. This reconstruction process involves allocating memory for various graphical and text objects required to display the annotation correctly on the user interface.
The core technical flaw lies in how the software handles the lifecycle of these allocated objects during the rendering pipeline. Specifically, when processing the malformed font data associated with rich-text annotations, the application incorrectly manages object references. It releases or deallocates a specific memory object prematurely while retaining pointers to that same object for subsequent operations. This creates a classic use-after-free condition where the program attempts to access and utilize memory that has already been returned to the system allocator. Because the memory may have been reallocated for other purposes or simply marked as free, accessing it leads to undefined behavior. In this specific instance, the immediate consequence is an application crash due to invalid memory access, which disrupts service availability for the end user.
From a security architecture perspective, this vulnerability aligns with CWE-416, Use After Free, which describes situations where pointers are used after they have been freed, leading to unpredictable behavior and potential exploitation beyond simple denial of service. The manipulation of rich-text attributes suggests an attempt to exploit parsing logic errors that can be triggered remotely via a malicious document delivered through email or web downloads. While the immediate observation is a crash indicating a Denial of Service impact as defined by ATT&CK technique T1499, use-after-free vulnerabilities are frequently precursors to more severe exploits such as arbitrary code execution if an attacker can control the data written into the freed memory region before it is reallocated. The presence of script execution in the trigger path further highlights the complexity of the attack surface within PDF parsers that support dynamic content and scripting capabilities.
Mitigation strategies for this vulnerability require both immediate patching by the vendor to correct the object lifecycle management logic and proactive defensive measures by organizations. Users should ensure their Foxit software is updated to the latest version where memory handling routines have been hardened against premature deallocation. In environments where updating may not be immediately feasible, deploying application whitelisting or restricting the execution of scripts within PDF readers can reduce the attack surface. Additionally, network-level controls such as sandboxing email attachments and using advanced threat protection solutions that analyze document behavior before delivery to endpoints can prevent exposure to these crafted files. Security teams should monitor for indicators of compromise related to abnormal memory usage patterns in Foxit processes, which may indicate attempted exploitation attempts targeting this specific parsing flaw.