Fix non-functional DNS brute-force canary check

[aconite33]

Summary

Fixes #3004 -- three bugs that made the canary-based false-positive detection in brute.py completely non-functional:

• Exhausted generator: The canaries generator was consumed by list() on line 61, then reused for in membership checks on line 71 which always returned False. Replaced with a set built from the already-materialized list for correct (and O(1)) lookups.
• Trailing dot: hostname.split(domain)[0] produces a trailing dot (e.g. "sub.") that never matched canary strings like "sub". Added .rstrip(".") to normalize the extracted subdomain.
• Variable shadowing: The for domain, rdtypes in wildcard_domains.items() loop overwrote the domain function parameter, which corrupted the abort warning message. Renamed the loop variable to wildcard_domain.

Impact

On wildcard domains, massdns returns results for every queried subdomain including canaries. The canary safety net is supposed to detect this and abort, but the three bugs above prevented it from ever triggering. This caused scans to flood with thousands of false-positive DNS_NAME events and wildcard detection log entries.

Changes

• bbot/core/helpers/dns/brute.py -- all three bug fixes
• bbot/test/test_step_1/test_dns.py -- unit test that validates the canary check logic (exhausted generator, trailing dot, variable shadowing, and end-to-end canary detection)

Test plan

• New test_dnsbrute_canary_check unit test passes
• Run full test suite
• Manual scan against a known wildcard domain to verify canaries trigger abort

[github-actions]

📊 Performance Benchmark Report

Comparing 3.0 (baseline) vs fix-dnsbrute-canary-check (current)

📈 Detailed Results (All Benchmarks)

📋 Complete results for all benchmarks - includes both significant and insignificant changes

🧪 Test Name	📏 Base	📏 Current	📈 Change	🎯 Status
Bloom Filter Dns Mutation Tracking Performance	4.21ms	4.18ms	-0.5% ⚪	✅
Bloom Filter Large Scale Dns Brute Force	17.42ms	17.35ms	-0.4% ⚪	✅
Large Closest Match Lookup	351.33ms	342.55ms	-2.5% ⚪	✅
Realistic Closest Match Workload	186.52ms	189.25ms	+1.5% ⚪	✅
Event Memory Medium Scan	1776 B/event	1776 B/event	+0.0% ⚪	✅
Event Memory Large Scan	1760 B/event	1760 B/event	+0.0% ⚪	✅
Event Validation Full Scan Startup Small Batch	405.82ms	404.23ms	-0.4% ⚪	✅
Event Validation Full Scan Startup Large Batch	580.04ms	562.80ms	-3.0% ⚪	✅
Make Event Autodetection Small	30.53ms	30.57ms	+0.2% ⚪	✅
Make Event Autodetection Large	311.26ms	313.59ms	+0.7% ⚪	✅
Make Event Explicit Types	13.69ms	13.62ms	-0.5% ⚪	✅
Excavate Single Thread Small	3.886s	3.933s	+1.2% ⚪	✅
Excavate Single Thread Large	9.441s	9.809s	+3.9% ⚪	✅
Excavate Parallel Tasks Small	4.066s	4.089s	+0.6% ⚪	✅
Excavate Parallel Tasks Large	7.157s	7.186s	+0.4% ⚪	✅
Is Ip Performance	3.17ms	3.20ms	+1.0% ⚪	✅
Make Ip Type Performance	11.52ms	11.59ms	+0.7% ⚪	✅
Mixed Ip Operations	4.50ms	4.56ms	+1.2% ⚪	✅
Typical Queue Shuffle	64.38µs	62.29µs	-3.2% ⚪	✅
Priority Queue Shuffle	731.91µs	695.73µs	-4.9% ⚪	✅

🎯 Performance Summary

✅ No significant performance changes detected (all changes <10%)

---

🐍 Python Version 3.11.15

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91%. Comparing base (8b02acb) to head (751df73).
⚠️ Report is 11 commits behind head on 3.0.

Files with missing lines	Patch %	Lines
...t/test_step_2/module_tests/test_module_dnsbrute.py	90%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             3.0   #3005    +/-   ##
======================================
- Coverage     91%     91%    -0%     
======================================
  Files        436     440     +4     
  Lines      37072   37250   +178     
======================================
+ Hits       33677   33748    +71     
- Misses      3395    3502   +107     

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[TheTechromancer]

Thanks for catching these bugs. However the tests don't actually test any of the fixed code. They need to exercise the actual module code in order to be valid.

This should be possible though our standard methods of subprocess output and DNS mocking.

[aconite33]

Thanks for catching these bugs. However the tests don't actually test any of the fixed code. They need to exercise the actual module code in order to be valid.

This should be possible though our standard methods of subprocess output and DNS mocking.

Got it. I've updated the tests to align with the current tests.