DKIM and vendor batch: dangling CNAMEs, verification TXT, key settings

[marmot7775]

• A DKIM selector CNAME into a domain nobody has registered fails the
  card and tops the plan (critical): whoever registers it can sign mail
  that passes DKIM, and DMARC, as the domain. A missing target in a live
  zone is an info line. Microsoft's unfilled rotation slot is not reported.
  Detection reads the NXDOMAIN's canonical name, so it costs no query; one
  NS lookup per dangling target checks the registrable domain.
• Apex verification tokens that only a mail service asks for (MS=,
  protonmail-verification, zoho-verification, mgverify, amazonses:,
  brevo-code:, klaviyo-site-verification, pardot=,
  atlassian-sending-domain-verification) feed the vendor panel as "TXT".
  google-site-verification is left out: mostly Search Console.
• t=y grades the DKIM card amber with a medium plan row; h= without
  sha256 grades it red with a critical row (RFC 8301 forbids SHA-1).
• DMARC Evaluation's DKIM row reads "does not apply" on a no-mail
  domain, matching the card (Doc 78 leftover).
• The vendor panel ignores -include:, ~include: and ?include:.

Live checks from marmot: no dangling targets outside Microsoft rotation slots on github.com, casper.com, allbirds.com, uber.com, booking.com, monday.com, rei.com, target.com (Microsoft's are suppressed by design), so the dangling paths are covered by tests/test_dkim_dangling_cname.py. Tests: 2212 locally (the two build-SHA tests fail only inside a git worktree).

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Vendor detection recognizes verification tokens in DNS TXT records, including providers such as Microsoft 365, Mailgun, and Amazon SES.
  • DKIM checks flag unregistered selector targets, test-mode keys, and keys that only support SHA-1, with remediation guidance and security priorities.
• Bug Fixes
  • SPF vendor detection respects include qualifiers.
  • DMARC results show DKIM as not applicable for no-mail domains without active DKIM selectors.
  • Vendor sources are displayed more clearly in reports and detection details.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 486482a and b2a135d.

📒 Files selected for processing (7)

• audit_engine.py
• spf_execution_engine.py
• spf_intelligence.py
• tests/test_dkim_dangling_cname.py
• tests/test_resilience_null_spf_row.py
• tests/test_vendor_patterns.py
• vendor_patterns.py

🚧 Files skipped from review as they are similar to previous changes (6)

• tests/test_vendor_patterns.py
• audit_engine.py
• tests/test_resilience_null_spf_row.py
• spf_intelligence.py
• spf_execution_engine.py
• tests/test_dkim_dangling_cname.py

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📝 Walkthrough

Walkthrough

The change expands vendor detection to use apex TXT verification tokens and filters SPF include qualifiers. DKIM analysis now reports dangling selector targets and key-setting findings. No-mail domains without DKIM selectors receive a not-applicable result. The app and PDF report display vendor sources, and static pages use updated asset versions.

Changes

Vendor detection

Layer / File(s)	Summary
Verification TXT and SPF detection vendor_patterns.py, advanced_fingerprinting.py, audit_engine.py, tests/test_vendor_patterns.py	Fingerprinting recognizes selected apex TXT verification tokens and passes them into vendor results. SPF includes with -, ~, or ? qualifiers do not produce vendor signals. Tests cover recognized tokens, evidence sources, and qualifier handling.
Vendor source display and static assets pdf_report.py, static/app.js, static/*.html, static/articles/*.html	Vendor source labels appear in the app and PDF report. Static page asset URLs use the updated cache-version query.

DKIM assessment

Layer / File(s)	Summary
Dangling selector discovery spf_intelligence.py, tests/test_dkim_dangling_cname.py	Selector discovery retains CNAME targets returned through NXDOMAIN responses and classifies them as stale or unregistered. Tests cover target classification and excluded cases.
DKIM card findings and remediation result_transformer.py, tests/test_dkim_dangling_cname.py, tests/test_dkim_key_settings.py	DKIM cards incorporate unregistered-target issues and analyze t=y and SHA-1-only keys. The security roadmap includes corresponding actions, and tests check the findings and remediation text.
No-mail DKIM result display spf_execution_engine.py, static/app.js, tests/test_resilience_null_spf_row.py	A no-mail domain without selectors receives a not-applicable DKIM result. The app displays that result neutrally and labels its alignment as “does not apply.”

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant SelectorProbe
  participant DNSResolver
  participant DKIMDiscovery
  participant DanglingClassifier as _classify_dangling
  participant DKIMTransformer as transform_dkim
  SelectorProbe->>DNSResolver: Query selector CNAME
  DNSResolver-->>SelectorProbe: NXDOMAIN with canonical target
  SelectorProbe->>DKIMDiscovery: Return dangling-selector record
  DKIMDiscovery->>DanglingClassifier: Classify target
  DanglingClassifier-->>DKIMDiscovery: Return target status
  DKIMDiscovery->>DKIMTransformer: Provide selector issues
  DKIMTransformer-->>DKIMTransformer: Update DKIM card and roadmap findings

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Suggested reviewers: claude

Merge Risk: ⚪ Minimal · up to b2a13

The changes add verification-token vendor signals and more specific DKIM findings. No material issue is established that should prevent merging, subject to normal checks.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to b2a13

The new dangling-target assessment treats DNS nonexistence as proof that a domain is available for registration, then recommends critical remediation. That can overstate takeover risk for registered domains without working DNS delegation. Exposure is limited to audit results and operator decisions; no new credential access or automatic DNS modification was identified.

Retained concerns

• Medium · security · inferred: The new classifier converts an NS NXDOMAIN response into a confirmed unregistered-domain status. Consumers then fail the DKIM card and issue a critical recommendation stating that anyone can buy the domain. DNS nonexistence does not establish registration availability: a registered but undelegated domain can also return NXDOMAIN. This newly introduced evidence-to-verdict contract can produce unsupported takeover claims and misdirect security remediation.

Security review details

Security Blast Radius

• inferred — A public caller can request an audit of a syntactically valid domain. Control over that domain's DNS can influence CNAME targets and induce the new registrable-domain NS checks. The identified concern affects audit verdicts and operator remediation decisions; the inspected path does not itself register domains, obtain signing credentials, or modify DNS.

Security Findings and Attack Paths

• inferred — A dangling selector whose target lies under a registered but undelegated domain can produce the same NS NXDOMAIN result as an available domain. The new consumer chain then asserts registration availability and prioritizes record removal. This is a supported diagnostic-integrity concern, not evidence that an actual domain takeover occurred.

Trust Boundaries and Controls

• observed — The existing HTTP entrypoint applies rate limiting, domain validation, atomic concurrent-audit reservation, and a wall-clock audit deadline. The new DNS classification operates behind these controls rather than creating a separate unrestricted endpoint.

Resilience and Maintainability Implications

• observed — Selector lists and classification verdicts are invocation-local; shared executors schedule work without sharing result ownership. Discovery can still omit unconsumed dangling futures at the live-key cutoff or timeout. The cutoff and live-key pass semantics predate this PR, so this remains a coverage limitation rather than an introduced security regression.

Hardening Proposals

• proposed — Keep DNS-negative targets as suspected takeover candidates unless independent registration-availability evidence supports a confirmed claim. Preserve the distinction between DNS nonexistence, registration state, and uncertainty in the result contract and remediation priority.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 37.25% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 51 functions across 12 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main changes: dangling DKIM CNAME detection, verification TXT vendor detection, and DKIM key settings.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 5

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Inline comments:
Review comments at @spf_execution_engine.py:
- Around line 308-309: Update the `is_no_mail` override for `dkim_result` so it
applies only when an explicit outbound no-mail declaration is present, not when
`is_no_mail` is derived from a null MX; preserve `not confirmed` when no
selectors are found and outbound sending is not prohibited.

Review comments at @spf_intelligence.py:
- Line 286: Update _classify_dangling to bound or parallelize NS lookups so
classification stays within the remaining audit deadline; report any targets not
classified before the deadline as indeterminate.
- Around line 283-290: Update the DNSException handling in the
registrable-domain NS lookup so timeouts and SERVFAIL set an indeterminate
status instead of leaving status as stale. Keep stale for a successful lookup
and unregistered for NXDOMAIN.
- Around line 279-280: Update the Microsoft 365 skip condition so it suppresses
the rotation finding only when one selector target is missing; check both
discovered selector slots before continuing, and report the finding when both
selector1 and selector2 targets are missing.

Review comments at @vendor_patterns.py:
- Around line 185-192: Update the vendor verification patterns in this list,
including `mgverify=`, `amazonses:`, and `pardot\d+=`, to match only when a
nonempty valid token value follows the prefix; ensure incomplete TXT records do
not trigger vendor detection or related SPF suggestions.

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• Configuration used: defaults
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📥 Commits

Reviewing files that changed from the base of the PR and between a6e812c and 486482a.

📒 Files selected for processing (22)

• advanced_fingerprinting.py
• audit_engine.py
• pdf_report.py
• result_transformer.py
• spf_execution_engine.py
• spf_intelligence.py
• static/404.html
• static/about.html
• static/app.js
• static/articles/dane.html
• static/articles/dmarcbis.html
• static/articles/dnssec.html
• static/articles/index.html
• static/articles/p-reject.html
• static/articles/spf-lookups.html
• static/index.html
• static/privacy.html
• tests/test_dkim_dangling_cname.py
• tests/test_dkim_key_settings.py
• tests/test_resilience_null_spf_row.py
• tests/test_vendor_patterns.py
• vendor_patterns.py

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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[marmot7775]

All five addressed in the latest commit: the evaluation row takes the DKIM card's outbound rule (dkim_not_applicable=sends_no_mail); NS failures are 'unknown' and the lookups run in parallel under one 3s budget; both Microsoft slots empty with no live Microsoft key is an info line, one empty slot stays silent; a verification prefix needs a token of 4+ characters. Tests added for each.