CVE-2026-91806 in PDF Editor
Summary
by MITRE • 09/23/2026
A use-after-free vulnerability exists in Foxit PDF Editor/Reader’s handling of PDF form fields. Embedded JavaScript may access form-field references after the corresponding fields have been released, resulting in an application crash.
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Analysis
by VulDB Data Team • 09/23/2026
The identified security flaw represents a critical memory management error within the document processing engine of Foxit PDF Editor and Reader, specifically targeting the lifecycle management of interactive form field objects. This vulnerability is classified as a use-after-free condition, which corresponds to CWE-416 in the Common Weakness Enumeration taxonomy. In this scenario, the application allocates memory for specific data structures representing PDF form fields but fails to properly invalidate or nullify pointers after these resources are deallocated. When an attacker crafts a malicious PDF document containing embedded JavaScript code, they can exploit this timing discrepancy by triggering actions that cause the original field objects to be freed while retaining active references within the script execution context.
The technical mechanism relies on the asynchronous nature of event handling and garbage collection in many scripting engines used for PDF processing. The embedded JavaScript may execute commands that reference form fields after their underlying C++ or native memory structures have been released back to the system heap. Because the application does not perform adequate bounds checking or pointer validation before accessing these stale references, it attempts to read from or write to invalid memory addresses. This misuse of freed memory leads directly to undefined behavior within the process space, typically manifesting as an immediate application crash due to access violations or segmentation faults.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1203, which covers Exploitation for Client Execution, although in its current described state, it primarily facilitates Denial of Service (DoS). The operational impact is severe for users who process untrusted documents, as the crash can disrupt workflow and potentially destabilize the host system if the memory corruption affects adjacent critical structures. While a simple crash indicates a DoS vector, use-after-free vulnerabilities are historically significant because they often serve as precursors to more dangerous remote code execution attacks. If an attacker can control the content of the freed memory region or manipulate heap allocation patterns through subsequent allocations, they may achieve arbitrary read/write primitives, allowing for full system compromise.
Mitigation strategies must focus on both immediate patching and long-term architectural improvements. Users should immediately apply vendor-provided updates that address this specific flaw in Foxit PDF Editor and Reader versions. From a defensive posture perspective, organizations should enforce strict policies regarding the execution of embedded JavaScript within PDF documents, utilizing application control solutions to block or sandbox such activities by default. Additionally, enabling advanced memory protection features on operating systems, such as Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR), can mitigate the exploitability of this vulnerability by making it significantly harder for attackers to predict memory layouts and execute malicious code following a crash. Regular security awareness training should also be conducted to ensure users do not open PDF files from untrusted sources, thereby reducing the attack surface exposed to such crafted documents.