Fix DNS rebinding bypass (#69)#73
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Hostnames that resolve to RFC-1918/loopback addresses (e.g. evil.com → 127.0.0.1) previously bypassed local_filter because the regex only matched literal IPs. After the regex check, resolve the hostname and reject any address that falls in a private range. Reuses the existing dns permission and browser.dns.resolve() call. Closes ACK-J#69 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Problem
The
local_filterregex incancel()only matches requests whose URL contains a literal local IP address orlocalhost. A hostname likeattacker.comthat resolves to127.0.0.1passes all checks unblocked:thirdParty: true— passes same-origin guardlocal_filterregex — no match (URL contains the hostname, not the IP)Reported in #69.
Fix
Added a pure
isPrivateIPv4(ip)helper that covers all RFC-1918, loopback (127.0.0.0/8), link-local (169.254.0.0/16), and 0.0.0.0 ranges.Updated the DNS resolution block to call
browser.dns.resolve()once and check both:The existing
dnspermission andbrowser.dns.resolve()usage are unchanged. Thelocal_filterregex is kept as a fast pre-filter for literal-IP URLs.Fail-open on DNS error — resolution failures (NXDOMAIN, captive portals, split-horizon DNS) allow the request through rather than breaking legitimate browsing.
Testing
Load the extension from source, open the browser console, and verify a domain with an A record pointing to 127.0.0.1 is blocked while a non-local domain is allowed.
Closes #69