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Implements RFC 6764 Section 8 security requirement to validate that discovered service endpoints remain within the same domain as the queried domain. This prevents DNS hijacking attacks where malicious DNS records redirect clients to attacker-controlled servers. Security Issue: Without domain validation, if DNS is hijacked, an attacker can redirect example.com to evil.hackers.are.us. Even with TLS and valid certificates for evil.hackers.are.us, credentials would be leaked to the attacker. RFC 6764 Section 8 states: "In the absence of a secure DNS option, clients SHOULD check that the target FQDN returned in the SRV record matches the original service domain that was queried. If the target FQDN is not in the queried domain, clients SHOULD verify with the user that the SRV target FQDN is suitable for use before executing any connections to the host." Implementation: 1. Added _is_subdomain_or_same() function to validate discovered domains - Allows same domain (example.com -> example.com) - Allows subdomains (example.com -> calendar.example.com) - Rejects different domains (example.com -> evil.com) 2. Applied validation to SRV record discovery - Checks hostname from SRV records - Logs warning and rejects if domain mismatch - Falls back to next discovery method 3. Applied validation to well-known URI redirects - Checks redirect Location header - Rejects redirects to different domains - Returns None to try alternative discovery 4. Updated security documentation - Removed TODO comment (now implemented) - Added RFC 6764 Section 8 reference - Documented domain validation mitigation Testing: - Doctests verify _is_subdomain_or_same() logic - Handles edge cases: subdomains, case sensitivity, trailing dots This provides defense-in-depth alongside TLS certificate verification. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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Resolves #574 - DNS service discovery should not cause redirections to other domains. That is a security risk unless using DNSSEC. --------- Co-authored-by: Claude <noreply@anthropic.com>
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Solves #574
🤖 Generated with Claude Code