CVE-2025-4538 in kkFileView
Summary
by MITRE • 05/11/2025
A vulnerability was found in kkFileView 4.4.0. It has been classified as critical. This affects an unknown part of the file /fileUpload. The manipulation of the argument File leads to unrestricted upload. It is possible to initiate the attack remotely. The exploit has been disclosed to the public and may be used. The vendor was contacted early about this disclosure but did not respond in any way.
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Analysis
by VulDB Data Team • 06/17/2025
CVE-2025-4538 represents a critical unrestricted file upload vulnerability in kkFileView version 4.4.0 that poses significant security risks to affected systems. This vulnerability exists within the file upload functionality of the application, specifically in the /fileUpload endpoint where the File argument is processed without adequate validation or sanitization measures. The flaw allows attackers to bypass normal file upload restrictions and potentially execute malicious code on the target system. The vulnerability has been publicly disclosed and is actively being used in the wild, making it particularly dangerous for organizations that have not yet patched their systems. Given that the vendor was notified early but failed to respond, organizations must assume that no official patch is forthcoming and should implement immediate defensive measures.
The technical nature of this vulnerability aligns with CWE-434, which describes the improper restriction of uploads of file containing code, a common weakness that enables attackers to upload malicious files that can be executed by the web application. This weakness is particularly dangerous because it can lead to arbitrary code execution, remote code execution, and complete system compromise. The vulnerability's remote exploitation capability means that attackers do not need physical access to the system or any authenticated sessions to exploit it. The flaw essentially allows an attacker to upload any type of file to the server, potentially including malicious scripts, executables, or web shells that can be executed by the web server or application.
The operational impact of CVE-2025-4538 extends beyond simple data theft or system disruption, as it can enable attackers to establish persistent access to affected systems. Once an attacker successfully uploads a malicious file, they can use it to create backdoors, escalate privileges, or launch further attacks against the internal network. This vulnerability can be leveraged as a stepping stone for more sophisticated attacks within the enterprise environment, particularly when combined with other exploitation techniques. The fact that the vulnerability is actively being used in the wild means that organizations are likely already experiencing attacks, making immediate remediation critical. The attack surface is particularly broad since file upload functionality is commonly used in web applications and often requires minimal privileges to exploit.
Organizations should implement multiple layers of defense to mitigate the risks associated with CVE-2025-4538. Immediate defensive measures include disabling file upload functionality for the affected endpoint or implementing strict file type validation and content checking mechanisms. Network-based controls such as web application firewalls should be configured to block suspicious file upload attempts and monitor for anomalous patterns in the /fileUpload endpoint. Access controls should be enforced to ensure that only authorized users can access the file upload functionality, and all file uploads should be scanned for malicious content before being processed or stored. Additionally, organizations should consider implementing file extension whitelisting, MIME type validation, and content inspection techniques to prevent the execution of malicious files. The vulnerability's classification as critical in the CVSS scoring system indicates that organizations should prioritize this remediation effort above other security issues and consider the potential for severe business impact if exploited.