CVE-2026-91813 in PDF Editor
Summary
by MITRE • 09/23/2026
A vulnerability in Foxit PDF Editor/Reader’s update mechanism allows an update package to be replaced between download and high-privilege extraction due to insufficient file locking and integrity validation. This could enable local attackers to execute arbitrary code with elevated privileges.
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Analysis
by VulDB Data Team • 09/23/2026
The identified vulnerability resides within the software update subsystem of Foxit PDF Editor and Reader, specifically targeting the mechanism responsible for downloading and installing application updates. The core technical flaw stems from a race condition inherent in the file handling process during the upgrade workflow. When an update package is downloaded to a temporary location on the local filesystem, there exists a critical time window between the completion of the download and the subsequent extraction or installation phase where elevated privileges are typically required. During this interval, the application fails to implement robust file locking mechanisms or perform sufficient integrity validation checks before proceeding with privileged operations. This lack of atomicity in the update process creates an opportunity for local attackers to intervene in the workflow by replacing the legitimate update package with a maliciously crafted payload while it resides in the temporary directory awaiting extraction.
From a technical perspective, this vulnerability is classified under CWE-367, which denotes Time-of-check to time-of-use (TOCTOU) race conditions. The attacker exploits the gap between the system verifying the presence of an update file and the moment that same file is accessed for execution or installation. Because Foxit PDF Editor often requires administrative rights to modify its own program files in protected directories such as Program Files, any code executed during this extraction phase inherits those high-level privileges. By substituting the expected binary with a malicious executable containing arbitrary commands, an attacker can leverage these elevated permissions to execute code on behalf of the user or system account running the application. This effectively bypasses standard security controls that rely on file integrity and exclusive access locks to prevent unauthorized modifications during critical operations.
The operational impact of this vulnerability is significant as it facilitates privilege escalation from a low-privilege local context to high-level administrative rights without requiring physical interaction with the target machine beyond initial placement of the malicious payload. An attacker who has gained limited user access on an affected system can exploit this flaw to gain full control over the environment, install persistent backdoors, exfiltrate sensitive data, or pivot to other systems within the network. This aligns closely with MITRE ATT&CK technique T1059, Command and Scripting Interpreter, specifically when combined with privilege escalation vectors such as T1068 Exploitation for Privilege Escalation. The ability to execute arbitrary code with elevated privileges undermines the confidentiality, integrity, and availability of the host system, potentially leading to complete compromise of organizational assets protected by that endpoint.
Mitigation strategies must focus on closing the race condition window through rigorous software engineering practices. Developers should implement strict file locking mechanisms using operating-system-level exclusive locks during the entire duration between download completion and extraction initiation. Additionally, integrity validation via cryptographic checksums or digital signatures should be performed immediately before any privileged operation to ensure the update package has not been tampered with since its initial verification. Users are advised to apply vendor-provided patches that address this specific flaw as soon as they become available. In environments where immediate patching is not feasible, restricting user permissions on temporary directories and monitoring for unusual file modifications in application-specific temp folders can provide a layer of defense against exploitation attempts until the underlying code defect is resolved.