* Extract shared DnsTestHelper from duplicated stub_dns_resolution methods
* Fix flaky WebTest by stubbing DNS resolution for push subscription creation
The SSRF filter checked ipv4_mapped? but not ipv4_compat?, allowing
addresses like ::169.254.169.254 to bypass the link-local check and
reach cloud metadata endpoints.
Changes:
- Add ipv4_compat? check to block deprecated IPv4-compatible format
- Rename private_address? to blocked_address? (more accurate - method
blocks more than just RFC 1918 private ranges)
- Add IPv6 test coverage for both mapped and compat formats
Both ipv4_mapped and ipv4_compat formats are blocked entirely as
defense-in-depth: DNS never returns these formats, so they only
appear in attack scenarios.
HackerOne: #3481701
Add SSRF protection for web push endpoints:
- Resolve endpoint IP once and pin it for connection
- Validate endpoints resolve to public IPs
- Whitelist permitted push service hosts
Add missing IP ranges to SsrfProtection:
- 100.64.0.0/10 (Carrier-grade NAT, RFC6598)
- 198.18.0.0/15 (Benchmark testing, RFC2544)
Note: link-local (169.254.0.0/16) is already covered by ip.link_local?
Mike Dalessio