Executive Summary

This vulnerability exists in FastGPT versions 4.14.11 and earlier. The function isInternalAddress() is designed to block access to cloud metadata endpoints by checking URLs against a hardcoded blocklist using a fullUrl.startsWith() method. However, this check can be bypassed using at least seven different URL encoding techniques that still resolve to the same cloud metadata service but do not match the blocklist patterns.

Additionally, the broader private IP address checks (isInternalIPv4 and isInternalIPv6) are disabled by default because the CHECK_INTERNAL_IP setting defaults to false. This means that these bypasses can reach the metadata endpoint without any further validation or blocking.

At the time of publication, no public patches are available to fix this issue.

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Impact Analysis

This vulnerability allows an attacker to bypass protections and access cloud metadata endpoints that should be blocked. Since cloud metadata services often contain sensitive information such as credentials, configuration details, or tokens, unauthorized access could lead to information disclosure.

The CVSS score of 7.7 (High severity) with a vector indicating network attack with low complexity and requiring low privileges suggests that an attacker with some access could exploit this vulnerability remotely without user interaction.

While the vulnerability does not impact integrity or availability, the high confidentiality impact means sensitive data could be exposed, potentially leading to further attacks or unauthorized access.

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Mitigation Strategies

At the time of publication, there are no publicly available patches for this vulnerability.

Since the vulnerability involves bypassing the isInternalAddress() function's URL blocking via multiple URL encoding techniques, immediate mitigation steps could include implementing additional network-level controls to restrict access to cloud metadata endpoints.

Also, enabling or enforcing broader private IP checks (such as isInternalIPv4/isInternalIPv6) if configurable, might help reduce exposure, although by default these checks are disabled.

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