imgproxy is vulnerable to SSRF against 0.0.0.0

Summary

Imgproxy does not block the 0.0.0.0 address, even with IMGPROXY_ALLOW_LOOPBACK_SOURCE_ADDRESSES 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.