CVE-2026-91809 in PDF Editor
Summary
by MITRE • 09/23/2026
A use-after-free vulnerability exists in Foxit PDF Editor/Reader’s handling of malformed PDF form fields. Improper validation during field-name traversal may cause the application to access a released object, 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 logic responsible for parsing and validating form fields in Portable Document Format files. This vulnerability is classified as a use-after-free condition, which falls under the Common Weakness Enumeration category CWE-416. In this scenario, an attacker can craft a malicious PDF document containing specially constructed malformed form field definitions that exploit improper validation during the traversal of field names. The core technical failure lies in the application's inability to correctly track the lifecycle of memory objects associated with these fields. When the parser processes the corrupted data structure, it fails to ensure that previously allocated resources are properly retained or nullified after they have been logically removed from active use, leading to a state where pointers reference deallocated memory regions.
From an operational perspective, this vulnerability allows for remote code execution potential if exploited with additional techniques such as heap spraying or specific exploitation primitives, although the immediate observable impact is often limited to application instability and denial of service. The direct consequence described in the initial report is an application crash, which disrupts user workflow and can lead to data loss if unsaved work is involved. However, because use-after-free vulnerabilities provide arbitrary read and write capabilities over freed memory blocks, a sophisticated attacker could leverage this flaw to execute arbitrary code on the victim's system with the privileges of the affected process. This aligns with MITRE ATT&CK technique T1203, which covers exploitation for client execution, highlighting the severity beyond simple denial of service.
The root cause stems from insufficient validation checks during the parsing phase where field names are traversed and processed. The software does not adequately verify whether a memory block referenced by a form field pointer has already been freed or is still valid before attempting to access its properties. This lack of rigorous state management allows the application to proceed with operations on invalid pointers, triggering undefined behavior that typically manifests as a segmentation fault or general protection fault in modern operating systems. Such errors are particularly dangerous because they can be triggered simply by opening a malicious file, requiring no user interaction beyond viewing the document within the compromised software environment.
To mitigate this risk, it is imperative to apply the latest security patches and updates provided by Foxit Software immediately upon release. These updates typically include fixes that enforce stricter memory management protocols, ensuring that pointers are invalidated after deallocation and that all field name traversals perform comprehensive validity checks before accessing object properties. Additionally, organizations should implement application whitelisting or sandboxing solutions to limit the potential impact of any successful exploitation by restricting the permissions granted to PDF viewing applications. Users should also be educated on the risks associated with opening documents from untrusted sources, as this vulnerability highlights the importance of maintaining up-to-date software defenses against document-based attacks that target common productivity tools.