CVE-2026-91795 in PDF Editor
Summary
by MITRE • 09/23/2026
Foxit PDF Editor/Reader's FileOpen plugin did not adequately validate certain encryption metadata in specially crafted PDF files. This could leave an internal pointer in an invalid state, resulting in chained read and write access violations and potentially enabling arbitrary code execution.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified within the Foxit PDF Editor and Reader software stems from a critical flaw in the FileOpen plugin's handling of encryption metadata associated with specially crafted Portable Document Format files. As a specialized component responsible for managing encrypted content, this module failed to perform adequate validation on specific structural elements before processing them. This lack of rigorous input sanitization allows attackers to construct malicious PDF documents that contain malformed or deliberately corrupted encryption parameters. When the application attempts to parse these files, it proceeds with operations based on invalid assumptions about the data structure, leading directly to memory corruption issues rather than gracefully rejecting the untrusted input as expected in secure software design practices.
The technical core of this flaw involves an internal pointer being left in an invalid state due to the insufficient validation process. In C and C++ based applications like Foxit PDF Reader, pointers are fundamental to memory management, but they require strict bounds checking and integrity verification before dereferencing or modification. By bypassing these checks during the parsing of encryption metadata, the application allows for a scenario where subsequent operations attempt to access memory locations that have not been properly allocated or initialized. This results in chained read and write access violations, meaning the attacker can control both what data is being read from memory and what values are written back into it. Such conditions create a classic buffer overflow or out-of-bounds write environment, which provides the necessary primitives for an adversary to manipulate program execution flow.
The operational impact of this vulnerability is severe, as it potentially enables arbitrary code execution on the affected system. Once an attacker achieves control over memory writes through these access violations, they can overwrite critical data structures such as function pointers or return addresses within the application's stack or heap. This manipulation allows for the injection and subsequent execution of malicious shellcode during normal document viewing activities. Since PDF readers are frequently used to open documents received via email or downloaded from untrusted sources, this vulnerability presents a high-risk attack vector that does not require user interaction beyond opening the file in many configurations. The ability to execute code with the privileges of the current user can lead to full system compromise, data exfiltration, and further lateral movement within an enterprise network environment.
From a classification perspective, this issue aligns closely with CWE-120 Buffer Copy without Checking Size of Input which describes cases where memory is copied into a buffer without verifying that the input fits within the allocated space. Additionally, the failure to validate encryption metadata before use relates to CWE-20 Improper Input Validation, highlighting the absence of robust checks on data integrity prior to processing. In terms of tactical mapping under the MITRE ATT&CK framework, this vulnerability facilitates initial access through vector components such as Spearphishing Attachment or Drive-by Compromise, where malicious PDFs are delivered to victims. The exploitation technique leverages memory corruption primitives typical of exploit development strategies aimed at bypassing modern operating system protections like ASLR and DEP by achieving precise control over instruction pointers.
Mitigation for this vulnerability requires immediate application of vendor-provided patches that address the input validation logic within the FileOpen plugin. Organizations should prioritize updating Foxit PDF Editor and Reader to versions where these specific encryption metadata checks have been hardened against malformed inputs. In environments where patching is not immediately feasible, network-level controls such as deep packet inspection or sandboxed document viewing services can be employed to neutralize malicious payloads before they reach end-user workstations. Furthermore, implementing application whitelisting policies and restricting the execution of scripts within PDF readers can reduce the blast radius if an exploitation attempt occurs. Regular security awareness training for users regarding suspicious attachments remains a vital complementary defense layer against social engineering tactics that often accompany such exploits.