CVE-2026-91790 in PDF Editor
Summary
by MITRE • 09/23/2026
When rendering the page image, Foxit PDF Editor/Reader fails to perform validation on image objects whose optional content attributes are malformed. As a result, the program may access an already-freed internal data structure, triggering a crash due to UAF.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified in Foxit PDF Editor and Reader stems from insufficient input validation during the rendering process of page images, specifically concerning objects with optional content attributes that are malformed or corrupted. In complex document formats like PDF, optional content groups allow for layers within a document to be shown or hidden based on user interaction or specific conditions. When an application processes these structures, it must rigorously validate the integrity and consistency of all associated metadata before attempting to render them visually. The flaw arises because the software fails to adequately verify the state and validity of internal data structures linked to these optional content attributes prior to accessing them for rendering purposes. This lack of validation creates a scenario where the application proceeds with operations on memory regions that are no longer valid or have been deallocated by other parts of the system, leading directly to a use-after-free condition.
From a technical perspective, this is classified as CWE-416: Use After Free, which occurs when software continues to use a pointer after it has been freed, typically resulting in unstable behavior such as crashes, data corruption, or arbitrary code execution depending on how the memory is reallocated and used by subsequent operations. In the context of PDF rendering engines, image objects often involve complex memory management routines where buffers are allocated for temporary processing and then released once the visual representation is generated. If an attacker crafts a malicious PDF file containing specially constructed optional content attributes that trigger premature or inconsistent deallocation while other processes still hold references to those same memory addresses, the application will attempt to read from or write to this freed memory space. The result of such an operation is unpredictable but frequently manifests as a denial-of-service condition due to immediate program termination caused by segmentation faults or access violations when the operating system detects invalid memory access.
The operational impact of this vulnerability primarily centers on stability and availability, although it poses potential risks for more severe exploitation if the use-after-free state can be manipulated to achieve arbitrary code execution. For end-users opening untrusted documents, the immediate consequence is a crash of the PDF viewer or editor application, leading to loss of unsaved work and disruption of workflow. While denial-of-service is the most direct outcome, security researchers often note that modern memory corruption vulnerabilities like use-after-free are frequently chained with other techniques such as heap spraying or control flow hijacking to escalate privileges or execute remote code. Therefore, even if the primary observed effect is a crash, the underlying flaw represents a significant security risk because it compromises the integrity of the application's execution environment and could potentially be leveraged by an attacker targeting specific versions of the software with known memory layout characteristics.
Mitigation strategies for this vulnerability involve both immediate patching and long-term defensive coding practices. The most effective remediation is to apply the latest updates provided by Foxit Software, which include fixes that enforce strict validation checks on optional content attributes before any rendering operations are initiated. These patches likely introduce additional boundary checks and state verification routines to ensure that memory references remain valid throughout the lifecycle of the image object processing. Beyond software updates, organizations should implement application whitelisting or sandboxing solutions to limit the impact if a user inadvertently opens a malicious document. Furthermore, developers working on similar PDF parsing libraries should adopt secure coding standards such as those outlined in OWASP guidelines for input validation and memory management, ensuring that all external inputs are sanitized and that pointer lifecycles are strictly managed to prevent dangling references from ever being dereferenced.