Executive Summary

This vulnerability in GravCMS 1.10.7 allows remote attackers to write or update arbitrary YAML configuration files without authentication by exploiting the scheduler endpoint. Attackers manipulate the 'admin-nonce' parameter to inject base64-encoded payloads, which lets them create malicious custom jobs that execute arbitrary system commands, including PHP code execution. This enables attackers to gain initial access and execute code remotely without any privileges or user interaction. [1, 3]

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Impact Analysis

The vulnerability can have a severe impact by allowing attackers to execute arbitrary PHP code and system commands remotely without authentication. This can lead to unauthorized access, data compromise, system manipulation, and potentially full control over the affected GravCMS server. The CVSS v4 score of 9.3 indicates a critical severity with high impact on confidentiality, integrity, and availability. [1, 3]

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Detection Guidance

This vulnerability can be detected by monitoring HTTP requests to the GravCMS scheduler endpoint, specifically looking for suspicious POST requests to /admin/config/scheduler that include the admin-nonce parameter with base64-encoded payloads. One detection method is to inspect web server logs for such requests. Additionally, you can use network monitoring tools to detect unusual outbound connections or scheduled jobs executing unexpected commands. Since the exploit involves creating malicious scheduler jobs, checking the GravCMS scheduler configuration files for unauthorized or suspicious YAML entries is recommended. There is a known Python3 script exploit that extracts the admin-nonce and sends crafted POST requests; reviewing logs for similar patterns can help detect exploitation attempts. [3]

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Mitigation Strategies

Immediate mitigation steps include restricting access to the GravCMS admin endpoints, especially /admin/config/scheduler, to trusted IP addresses or networks. Applying any available patches or updates from GravCMS that address this vulnerability is critical. If patches are not yet available, disabling or restricting the scheduler functionality temporarily can reduce risk. Monitoring and removing any suspicious custom scheduler jobs from the configuration is also advised. Implementing web application firewalls (WAF) rules to block requests containing suspicious admin-nonce parameters or base64-encoded payloads can help prevent exploitation. [1]

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