CVE-2026-91805 in PDF Editor
Summary
by MITRE • 09/23/2026
A use-after-free vulnerability exists in Foxit PDF Editor/Reader’s PDF page-tree handling. A specially crafted PDF can trigger page-structure changes during rendering, causing the application to access released page objects and resulting in memory corruption and an application crash.
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Analysis
by VulDB Data Team • 09/23/2026
The identified security flaw represents a critical use-after-free vulnerability located within the core document object model of Foxit PDF Editor and Reader, specifically affecting the logic responsible for managing the PDF page tree structure. This type of error occurs when software continues to reference memory that has already been deallocated by the system or garbage collector. In this specific instance, the vulnerability is triggered during the rendering process of a maliciously crafted Portable Document Format file. The attacker constructs a PDF document with carefully manipulated structural elements designed to exploit race conditions or logical errors in how Foxit handles page references and memory allocation for those pages.
When an end-user opens or renders this specially crafted PDF, the application attempts to parse the complex page-tree structure defined within the file. During this parsing phase, certain operations cause changes to the internal representation of the document's pages. These structural modifications inadvertently lead to the premature release of specific page objects from memory while other parts of the application still maintain active references or pointers to those same objects. Consequently, when subsequent rendering commands attempt to access these now-dangling pointers, they interact with freed memory regions that may have been reallocated for different purposes by the operating system or overwritten by unrelated data processes.
The operational impact of this vulnerability is severe and multifaceted. The immediate consequence is often a denial of service manifested as an application crash due to segmentation faults or access violations resulting from invalid memory reads. However, in more sophisticated exploitation scenarios involving heap manipulation techniques such as heap spraying or controlled overwrites, the use-after-free condition can be leveraged to achieve arbitrary code execution on the victim's system. This allows attackers to bypass standard security mitigations and execute malicious payloads with the privileges of the user running the PDF reader software. Such exploits are particularly dangerous because they target widely used productivity tools that users trust implicitly when opening documents received via email or downloaded from untrusted sources.
From a classification perspective, this vulnerability aligns closely with CWE-416, which defines use-after-free errors where pointers to freed memory are dereferenced. It also relates to CWE-362 regarding concurrent execution race conditions if the issue stems from timing-dependent logic in thread-safe operations within the PDF parser. In terms of offensive security frameworks like MITRE ATT&CK, this vulnerability facilitates initial access and potentially privilege escalation through techniques associated with client-side exploitation, specifically leveraging vulnerabilities in applications that handle untrusted data inputs without sufficient validation or safe memory management practices.
To mitigate the risks associated with this flaw, organizations must ensure that all instances of Foxit PDF Editor and Reader are updated to the latest patched versions released by the vendor. These updates typically include rigorous input sanitization for page-tree structures and improved lifecycle management for internal objects to prevent premature deallocation while references remain active. Additionally, implementing application whitelisting or sandboxing solutions can restrict the permissions granted to PDF readers, limiting the potential impact of any successful exploitation attempt. Security awareness training should also be conducted to educate users on the risks associated with opening documents from unknown origins, serving as a secondary layer of defense against social engineering tactics often paired with such technical exploits.