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http storage: pin the connection when blockPrivateIPs is enabled - #336

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presendapp:http-blockprivateips-connection-pinning
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presendapp:http-blockprivateips-connection-pinning

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@presendapp presendapp commented Sep 17, 2026

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Closes the TOCTOU/DNS-rebinding gap that validatePublicIP's own doc comment already disclosed: the hostname is resolved a second, separate time when fetch() opens the socket, so a record with a short TTL could answer publicly at check time and privately at connect time.

Adds getPinnedFetch(): a Node-only, lazily loaded undici Agent whose connector lookup hook re-validates every resolved address against the existing isPublicIP() check before it's ever handed to the connector -- resolution and validation happen inside the hook itself, so the addresses that were checked are the only ones the socket can connect to. Falls back to the plain global fetch if undici's Agent can't be loaded, matching the fail-open posture already used elsewhere in this file for optional platform features -- the existing per-call validatePublicIP check still applies either way.

Wired into both fetchURL() call sites, only when blockPrivateIPs is on, so behavior is unchanged with the option off.

New test mocks dns.promises.lookup (the pre-check) and the raw dns.lookup (used only by the new pinned connector) to answer differently for the same hostname -- a direct simulation of DNS rebinding -- and confirms the request is still rejected.

Verified locally:

  • tsc --noEmit, eslint, prettier all clean
  • vitest run test/storage/http.test.ts: 90/90 passing (89 pre-existing + 1 new)
  • Full suite: passes aside from one pre-existing, unrelated timeout in test/index.test.ts (confirmed it reproduces identically on main without this change, before opening this PR)

Summary by CodeRabbit

  • Bug Fixes
    • Improved protection against private and loopback addresses when private-IP blocking is enabled.
    • Network connections remain tied to the address validated before the request, preventing DNS changes from bypassing address checks.
    • Blocked-address errors now provide clearer details about the rejected address.
    • If enhanced address validation is unavailable, requests now fail safely instead of bypassing private-IP protection.
  • Compatibility
    • Node.js 20.18.1 or newer is now required for Node 20 users.

validatePublicIP() correctly resolves and checks a hostname before
fetching, but its own doc comment already disclosed the remaining gap
honestly: the name is resolved a second, separate time when fetch()
actually opens the socket, so a record with a short TTL could answer
publicly at check time and privately at connect time (DNS rebinding).

Adds getPinnedFetch(): a Node-only, lazily loaded undici Agent whose
connector lookup hook re-validates every resolved address against the
same isPublicIP() check before it is ever handed to the connector --
resolution and validation happen inside the hook itself, so the
addresses that were checked are the only ones the socket can connect
to. Falls back to the plain global fetch if undici's Agent can't be
loaded (non-Node runtime, or undici unavailable), same fail-open
posture already used elsewhere for optional platform features -- the
existing per-call validatePublicIP check still applies either way.

Wired into both fetchURL() call sites, only when blockPrivateIPs is
on, so behavior is unchanged with the option off.

New test mocks dns.promises.lookup (the pre-check) and the raw
dns.lookup (used only by the new pinned connector) to answer
differently for the same hostname -- a direct simulation of DNS
rebinding -- and confirms the request is still rejected. All 90 tests
in this file pass, including the 89 pre-existing ones; full suite
passes too aside from one pre-existing, unrelated timeout in
test/index.test.ts (reproduces identically on main, confirmed before
this change).
@presendapp
presendapp requested a review from pi0 as a code owner September 17, 2026 12:37
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📝 Walkthrough

Walkthrough

The HTTP storage path now uses an Undici dispatcher to validate DNS results at connection time when private-IP blocking is enabled. Tests cover the nested error cause and DNS-rebinding protection.

Changes

HTTP DNS pinning

Layer / File(s) Summary
Pinned fetch implementation
package.json, src/storage/http.ts
Adds undici, raises the minimum Node 20 version, and adds a cached fetch that validates connector DNS results with isPublicIP. The implementation fails closed when required support is unavailable and uses global fetch when private-IP blocking is disabled.
Protected request integration and tests
src/storage/http.ts, test/storage/http.test.ts
Uses the pinned fetch for direct requests and manual redirects when private-IP blocking is enabled. Tests verify the nested error cause and DNS-rebinding protection.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to d22f4

This update only raises the minimum supported Node.js version in package.json to align with a dependency requirement from earlier work in this change; it does not alter runtime behavior. There is no indication of new risk introduced by this increment, and it should be safe to merge.

🚥 Pre-merge checks | ✅ 5
✅ Passed checks (5 passed)
Check name Status Explanation
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check ✅ Passed The title clearly and concisely describes the main change: pinning HTTP connections when blockPrivateIPs is enabled.
Docstring Coverage ✅ Passed Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files. (1 skipped: 1 …
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: 2

🤖 Prompt for all review comments with AI agents
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Inline comments:
In `@package.json`:
- Line 34: Align the Node engine requirement in package.json with the resolved
undici@7.29.1 dependency by raising the Node 20 minimum from 20.16.0 to 20.18.1,
while preserving the existing engine range format.

In `@src/storage/http.ts`:
- Around line 430-431: Update getPinnedFetch so both fallback branches throw
IPX_IP_CHECK_UNAVAILABLE when blockPrivateIPs is enabled and connection-pinning
support is unavailable, instead of returning global fetch; preserve the existing
fetch fallback when private-IP blocking is disabled.

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Comment thread package.json
Comment thread src/storage/http.ts
When blockPrivateIPs is enabled, getPinnedFetch previously fell back to
the plain global fetch if node:dns or undici's Agent could not be
loaded, relying on the per-call validatePublicIP check alone. That
check does not bind the later socket connection, so a DNS-rebinding
attack could still connect to a private address in that fallback path.

Both fallbacks now throw IPX_IP_CHECK_UNAVAILABLE when blockPrivateIPs
is enabled and pinning cannot be set up, matching the existing
fail-closed behavior used elsewhere in this file when node:net /
node:dns are unavailable.

Addresses CodeRabbit review comment on unjs#336.
…6.0 -> 20.18.1)

Per CodeRabbit review: undici@7.29.1 requires Node >=20.18.1, but the
engines field still allowed 20.16.0. Verified: tsc --noEmit, eslint,
prettier all clean; vitest run test/storage/http.test.ts: 90/90 passing.
@presendapp

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Addressed the remaining CodeRabbit suggestion: package.json engines now requires Node >=20.18.1 (was 20.16.0), matching what undici@7.29.1 actually needs. Re-verified locally: tsc --noEmit, eslint, prettier all clean; vitest run test/storage/http.test.ts: 90/90 passing.

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