PromptHub's authenticated POST /api/skills/fetch-remote endpoint fetches URLs provided by users and returns the response body. The SSRF protection mechanism attempts to block private and loopback IP addresses by checking IPv6 addresses, but it fails to handle alternate valid IPv6 representations, including IPv4-mapped IPv6 addresses in hex form and non-literal forms of ::1. This allows authenticated users to bypass the SSRF filter and access internal network resources. The issue affects versions from 0.4.9 to before 0.5.4 and has been patched in version 0.5.4.

An attacker with authenticated access can exploit this SSRF vulnerability to make the server perform requests to internal or private network addresses that should be inaccessible. This can lead to unauthorized information disclosure (high confidentiality impact) and limited integrity impact. There is no direct availability impact. If the deployment allows open registration, any internet user can register and exploit this vulnerability.

This vulnerability has been patched in PromptHub version 0.5.4. Users should upgrade to version 0.5.4 or later to remediate this issue. No other vendor advisory or patch information is provided, so patch status beyond this is not confirmed. Until upgrading, restrict user registration or authenticated access to trusted users to reduce risk.