Executive Summary

CVE-2025-66844 is a Server-Side Request Forgery (SSRF) vulnerability in the Grav CMS that occurs when Twig templates process page content and the configuration allows undefined PHP functions to be registered. If the configuration option `system.twig.undefined_functions` is enabled, an attacker can exploit this by invoking PHP functions like `curl_exec` or `stream_socket_client` within Twig templates. This enables the attacker to make arbitrary HTTP requests from the server to internal or private network addresses, potentially accessing internal services that should not be exposed. [1]

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Impact Analysis

This vulnerability can allow an attacker to make unauthorized HTTP requests from the server to internal or private network endpoints. This can lead to exposure of sensitive internal APIs, metadata services, or other protected resources that are normally inaccessible from outside the network. The impact severity ranges from medium to high depending on the sensitivity of the internal services that can be accessed via SSRF. [1]

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Detection Guidance

Detection of this SSRF vulnerability involves checking if the Grav CMS configuration enables undefined PHP functions in Twig templates (specifically if `system.twig.undefined_functions` is enabled) and if template processing is active. You can inspect the Grav configuration files for this setting. Additionally, monitoring for unusual outgoing HTTP requests from the server to internal IP addresses (e.g., 127.0.0.1) can indicate exploitation attempts. Commands to help detect this include: 1) Checking Grav configuration: `grep -r 'undefined_functions' /path/to/grav/user/config/` 2) Monitoring network connections for suspicious internal requests: `netstat -anp | grep ESTABLISHED` or using `tcpdump` to capture HTTP requests originating from the Grav server to internal IPs, e.g., `tcpdump -i eth0 host 127.0.0.1 and tcp port 80` 3) Reviewing Twig templates for usage of PHP functions like `curl_exec` or `stream_socket_client` that could be exploited. [1]

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Mitigation Strategies

Immediate mitigation steps include disabling the configuration option `system.twig.undefined_functions` to prevent undefined PHP functions from being registered and used in Twig templates. Additionally, review and restrict Twig templates to avoid usage of potentially dangerous PHP functions such as `curl_exec` or `stream_socket_client`. Applying strict input validation and sanitization on templates and content processed by Twig is recommended. If possible, update Grav CMS to a version where this vulnerability is patched or apply custom patches to restrict exposure of network-related PHP functions. Monitoring and blocking outgoing requests to internal network addresses from the Grav server can also help mitigate exploitation. [1]

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Compliance Impact

The provided resources do not specify how this SSRF vulnerability in Grav CMS affects compliance with common standards and regulations such as GDPR or HIPAA.

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