Add central helper for ssrf address protection

src/pretix/helpers/ssrf.py

@@ -0,0 +1,19 @@
+import ipaddress
+
+
+_cgnat_net = ipaddress.ip_network('100.64.0.0/10')
+
+
+def should_block_access(sa):
+    ip_addr = ipaddress.ip_address(sa[0])
+    check_ip4 = ip_addr.ipv4_mapped if getattr(ip_addr, "ipv4_mapped", None) else ip_addr
+    if ip_addr.is_multicast:
+        return True, f"Request to multicast address {sa[0]} blocked"
+    if ip_addr.is_loopback or ip_addr.is_link_local:
+        return True, f"Request to local address {sa[0]} blocked"
+    if ip_addr.is_private:
+        return True, f"Request to private address {sa[0]} blocked"
+    if check_ip4 in _cgnat_net:
+        return True, f"Request to RFC 6598 address {sa[0]} blocked"
+
+    return False, None