[BUG] WebFetch blocked by egress proxy for custom domains — x-deny-reason: host_not_allowed

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Description

Claude Code's WebFetch tool cannot access websites hosted on Vercel (and likely other platforms) due to the egress proxy's allowed_hosts restriction. Requests are blocked before they ever reach the target server.

Investigation

• Verified the target site has no bot blocking (Cloudflare Bot Fight Mode off, no WAF rules, no Vercel Firewall)
• Cloudflare is DNS-only (not proxying) — Security Events show zero blocked requests
• The 403 with Server: envoy and x-deny-reason: host_not_allowed matches the exact pattern from #15583, confirming this is the egress proxy, not the target server

Impact

Users cannot use Claude Code to read or analyze their own websites. This affects any AI-assisted workflow involving marketing sites, documentation sites, or public web content.

Expected behavior

WebFetch should be able to access public websites without domain-specific allowlisting in the egress proxy.

Related

• #15583 (same root cause — egress proxy allowed_hosts restriction)

What Should Happen?

WebFetch should be able to access any public website. The egress proxy should not require domain-specific allowlisting for public URLs that the user explicitly requests via WebFetch.

Error Messages/Logs

## Error


HTTP 403
Server: envoy
x-deny-reason: host_not_allowed

Steps to Reproduce

Reproduction

1. In a Claude Code web session, use WebFetch to access any custom domain
2. Also fails on the .vercel.app deployment URL
3. The request never reaches the target — blocked at the egress proxy layer

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.89

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

On Claude Code Web and Mobile only.