CVE-2026-91803 in PDF Editor
Summary
by MITRE • 09/23/2026
A local privilege escalation vulnerability exists in the updater of Foxit PDF Editor/Reader due to unsafe loading of dynamic-link libraries from a user-writable directory during high-privilege operations. A local attacker could exploit this issue to execute code with elevated privileges.
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Analysis
by VulDB Data Team • 09/23/2026
The identified security flaw resides within the update mechanism of Foxit PDF Editor and Reader, specifically involving an insecure library loading practice that facilitates local privilege escalation. This vulnerability stems from a fundamental design error where the application attempts to load dynamic-link libraries (DLLs) from directories that are writable by standard, unprivileged users while operating with elevated system privileges. In Windows environments, when a process running as SYSTEM or Administrator searches for DLLs in user-controlled paths before checking secure system directories, it creates an opportunity for malicious actors to intercept the loading process. This specific flaw aligns closely with CWE-427, which describes Uncontrolled Search Path Element, and is further categorized under CWE-94, Improper Control of Generation of Code (Code Injection), as it allows external input to dictate code execution flow in a privileged context.
From an operational perspective, this vulnerability enables a local attacker who has already gained access to the system with low-level privileges to escalate their rights to those of the SYSTEM account or the currently logged-in user if they possess administrative credentials. The attack vector typically involves placing a malicious DLL file into one of the vulnerable directories that the updater checks during its initialization phase. When the Foxit updater executes, it inadvertently loads this attacker-controlled library instead of the legitimate component. Because the updater runs with high privileges, any code executed within the context of this malicious DLL inherits those same elevated permissions. This effectively bypasses standard access controls and allows the execution of arbitrary commands on the host system without triggering typical user consent prompts or security warnings associated with privilege escalation attempts.
The exploitation of this vulnerability is consistent with techniques documented in the MITRE ATT&CK framework, particularly under T1055, which covers Process Injection, and more specifically T1068, Exploitation for Privilege Escalation. An adversary leveraging this flaw would likely stage their payload by first establishing a foothold on the target machine through phishing or other initial access methods. Once inside, they would identify the presence of Foxit PDF Editor/Reader and locate the specific directory susceptible to DLL hijacking. By crafting a malicious library that mimics the expected interface but executes arbitrary code upon loading, the attacker can achieve persistent administrative control over the system. This level of access allows for the installation of backdoors, theft of sensitive data stored locally, lateral movement across networked systems using stolen credentials, and complete compromise of the endpoint's integrity.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most effective short-term solution is to apply vendor-provided patches that correct the library search path logic within the updater component. Organizations should prioritize updating Foxit PDF Editor/Reader to the latest version where this insecure loading behavior has been rectified, ensuring that DLLs are loaded only from trusted, non-writable system directories such as Program Files or System32. In environments where immediate patching is not feasible, administrators can implement file integrity monitoring on known vulnerable directories to detect unauthorized creation of executable files. Additionally, enforcing strict application control policies via Windows Defender Application Control or similar tools can prevent the execution of unsigned binaries from user-writable locations, thereby neutralizing the DLL hijacking vector even if the vulnerability remains unpatched in the software itself. Regular auditing of installed applications and their update mechanisms is essential to maintain a robust security posture against such privilege escalation threats.