CVE-2026-91789 in PDF Editor
Summary
by MITRE • 09/23/2026
Foxit PDF Editor/Reader’s U3D/GIF texture decoding path contained insufficient validation of image dimensions and related size information. Under certain conditions, this could lead to an incorrectly sized memory allocation and a subsequent out-of-bounds write during pixel processing, potentially resulting in remote code execution.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified in Foxit PDF Editor and Reader stems from a critical flaw within the U3D (Universal 3D) and GIF texture decoding subsystems. This component is responsible for parsing and rendering three-dimensional models and animated graphics embedded within Portable Document Format files, which are commonly encountered in both personal and enterprise workflows. The core technical deficiency lies in the insufficient validation of image dimensions and associated size metadata during the processing pipeline. When a maliciously crafted PDF file containing malformed U3D or GIF data is processed, the application fails to rigorously verify that the declared width and height parameters align with actual buffer constraints before proceeding with memory operations. This lack of rigorous boundary checking allows an attacker to supply dimension values that are disproportionately large relative to the available heap space or incorrectly calculated based on stride information.
This validation failure directly precipitates a heap-based out-of-bounds write condition during pixel processing. Specifically, when the application attempts to allocate memory for image buffers, it relies on the untrusted input dimensions without adequate sanity checks. Consequently, the system allocates a buffer that is smaller than what subsequent decoding routines expect or attempt to write beyond the allocated boundaries. As the decoder processes pixel data, it writes information past the end of the designated memory region. This out-of-bounds write corrupts adjacent heap metadata or overwrites critical control structures within the application's memory space. The corruption of these internal structures can be leveraged by an attacker to hijack program execution flow, potentially leading to arbitrary code execution with the privileges of the user running the vulnerable software.
From a threat modeling perspective, this vulnerability is classified under CWE-120 Buffer Copy without Checking Size of Input and CWE-787 Out-of-bounds Write within the Common Weakness Enumeration framework. These classifications highlight the fundamental failure in input validation and memory management practices that characterize many modern application security issues. In terms of offensive tactics, this flaw aligns with MITRE ATT&CK techniques related to Initial Exploitation and Defense Evasion, specifically involving exploitation for remote code execution via crafted documents. Attackers typically distribute such malicious PDF files through phishing campaigns or compromised websites, relying on social engineering to trick users into opening the file, thereby triggering the vulnerability without any further user interaction beyond the initial document open event.
The operational impact of this vulnerability is severe, as it enables remote code execution with minimal effort from an attacker. Once executed, the malicious payload can perform a wide range of destructive actions including data exfiltration, installation of additional malware such as ransomware or spyware, and establishing persistent backdoors within the victim's network environment. Given that Foxit PDF Editor is widely used in corporate environments for document creation and editing, successful exploitation could lead to significant organizational compromise, intellectual property theft, and disruption of business operations. The risk is further amplified by the ubiquity of PDF files as a standard communication format across industries.
To mitigate this risk, organizations should immediately apply vendor-provided security patches that address the validation logic in the U3D and GIF decoding paths. It is imperative to maintain up-to-date software versions where these specific memory management flaws have been corrected with stricter bounds checking and input sanitization routines. In environments where patching may be delayed due to compatibility concerns, network-level controls such as deep packet inspection or sandboxed document viewing services can help detect and block malicious PDF files before they reach end-user workstations. Additionally, implementing application whitelisting policies and restricting the execution of untrusted scripts within browser plugins associated with PDF viewers can provide an additional layer of defense against exploitation attempts. Regular security awareness training for employees regarding phishing tactics remains a crucial complementary measure to reduce the likelihood of initial document opening by malicious actors.