Executive Summary

CVE-2026-4999 is an unrestricted file upload vulnerability in the Z-9527 Admin software affecting versions up to a specific commit. The issue occurs in the uploadFile function of the /server/utils/upload.js file, where the fileType parameter is used to construct file paths without proper validation or sanitization.

Because the fileType parameter is not sanitized, attackers can perform directory traversal by including sequences like '..' in the fileType value. This allows them to write files outside the intended upload directory, potentially overwriting important files on the server.

Additionally, the filename is used as-is without safe renaming or sanitization, increasing the risk of overwriting critical files. The vulnerability can be exploited remotely by authenticated attackers, and the isImg parameter check for image files can be bypassed by omitting it, allowing upload of arbitrary file types.

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Impact Analysis

This vulnerability can allow an attacker to upload arbitrary files to the server in unauthorized locations by exploiting directory traversal in the fileType parameter.

Such unauthorized file uploads can lead to overwriting important files, potentially causing denial of service, data corruption, or enabling further attacks such as remote code execution if malicious scripts are uploaded.

Because the upload service may run with higher privileges and files can be placed outside the intended directories, the overall security and integrity of the server and application can be severely compromised.

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Detection Guidance

This vulnerability can be detected by monitoring and testing the `/upload` endpoint for unrestricted file upload attempts that exploit the `fileType` parameter for directory traversal.

You can attempt to upload a file using crafted requests that include directory traversal sequences (e.g., `..`) in the `fileType` parameter to see if files are written outside the intended directory.

Example commands using curl to test the vulnerability might include:

• curl -v -F "[email protected]" "http://target/upload?fileType=../tmp&isImg=false"
• curl -v -F "[email protected]" "http://target/upload?fileType=../../../../tmp&isImg=false"

Additionally, checking server logs for unexpected file writes outside the upload directory or unusual file paths can help detect exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include:

• Implement a server-side whitelist for the `fileType` parameter to restrict uploads to allowed directories only.
• Canonicalize and verify that resolved file paths remain within a fixed upload root directory to prevent directory traversal.
• Reject any directory traversal sequences or absolute paths in the `fileType` parameter.
• Generate safe server-side filenames instead of using client-supplied names to avoid overwriting important files.
• Validate uploaded file content by checking magic bytes and file size to ensure only expected file types are accepted.
• Store uploaded files outside the webroot to reduce the risk of direct web access.
• Run the upload service with least privilege to limit the impact of a successful exploit.

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Compliance Impact

The vulnerability allows authenticated attackers to upload arbitrary files to the server via an unsanitized fileType parameter, enabling directory traversal and potential overwriting of important files.

Such unauthorized file uploads and potential data manipulation can lead to unauthorized access, data breaches, or data integrity issues, which may violate compliance requirements under standards like GDPR and HIPAA that mandate protection of personal and sensitive data.

Failure to properly validate and restrict file uploads could result in exposure of sensitive information or disruption of services, thereby impacting the organization's ability to meet regulatory obligations for data security and privacy.

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