Egress protection

To resolve did:web and did:webvh, check domain linkage, read status lists and inspect MCP servers or agent cards, DID.is fetches URLs derived from your input. Every fetch follows these rules.

Rules

HTTPS only. URLs with credentials (user:pass@) are refused.
Public addresses only. Every DNS answer must be public. If any answer is in a blocked range, the request fails with 403 EGRESS_BLOCKED.
Pinned connections. The connection is made to the address that was checked. There is no second DNS lookup, so DNS rebinding cannot redirect it.
IP literals and loopback hostnames are refused in identifiers.
Redirects: at most 2, each checked again; never from HTTPS to HTTP.
Timeout: 4 seconds per upstream request.
Size limits: 1 MiB for documents and most resources; 4 MiB for did:webvh logs; 2 MiB for MCP responses; 512 KiB for agent cards.
TLS: the certificate chain, validity and host name are checked.

Blocked ranges

IPv4:

0.0.0.0/8        10.0.0.0/8       100.64.0.0/10    127.0.0.0/8
169.254.0.0/16   172.16.0.0/12    192.0.0.0/24     192.0.2.0/24
192.88.99.0/24   192.168.0.0/16   198.18.0.0/15    198.51.100.0/24
203.0.113.0/24   224.0.0.0/4      240.0.0.0/4      255.255.255.255/32

IPv6:

::/128           ::1/128          ::ffff:0:0/96    64:ff9b::/96
64:ff9b:1::/48   100::/64         2001::/32        2001:db8::/32
2002::/16        fc00::/7         fe80::/10        fec0::/10
ff00::/8

These cover loopback addresses, private networks, link-local and cloud metadata addresses, multicast, documentation ranges and IPv6 translation prefixes that could reach them.

Example

localtest.me is a public name that resolves to a loopback address:

curl https://did.is/api/v1/resolve/did:web:localtest.me

{
  "type": "https://did.is/problems#EGRESS_BLOCKED",
  "title": "Egress blocked",
  "status": 403,
  "code": "EGRESS_BLOCKED",
  "detail": "destination ::1 is inside the non-public range ::1/128"
}

(Abridged: the response also includes the trace.)