Summary

Imgproxy does not block the 0.0.0.0 address, even with IMGPROXYALLOWLOOPBACKSOURCEADDRESSES set to false. This can expose services on the local host.

Details

imgproxy protects against SSRF against a loopback address with the following check (source):

if !config.AllowLoopbackSourceAddresses && ip.IsLoopback() { return ErrSourceAddressNotAllowed }

This check is insufficient to prevent accessing services on the local host, as services may receive traffic on 0.0.0.0. Go's IsLoopback (source) strictly follows the definition of loopback IPs beginning with 127. 0.0.0.0 is not blocked.

A flaw has been found in imgproxy up to 4.0.17. Affected by this vulnerability is the function sanitizeElement of the file processing/svg/svg.go of the component SVG Handler. Executing a manipulation can lead to cross site scripting. It is possible to launch the attack remotely. The exploit has been published and may be used. The project was informed of the problem early through an issue report but has not responded yet.