fix: SSRF via unauthenticated plugin test-layer endpoint

[deucebucket]

Bug

In plugins.py (~lines 165-219), /api/plugins/test-layer accepts an arbitrary url_template in the POST body, makes the HTTP request server-side, and returns the full response body. /api/plugins/save-layer persists arbitrary URLs to config. No URL validation (scheme, host, private-range blocking) exists.

Impact

Any network-adjacent attacker can scan internal networks, access cloud metadata endpoints (169.254.169.254), or hit localhost services. The test-layer endpoint is a full SSRF proxy with response reflection.

Fix

• Validate URL schemes (only http/https)
• Block private/link-local/metadata IP ranges (10.x, 172.16-31.x, 192.168.x, 169.254.x, 127.x, ::1)
• Consider adding a simple auth check or rate limit

Severity

Critical — full SSRF with response reflection.

Found via pipeline logic audit.