fix(cors): prevent SSRF via DNS rebinding#4090
Merged
khassel merged 1 commit intoMagicMirrorOrg:developfrom Apr 4, 2026
Merged
fix(cors): prevent SSRF via DNS rebinding#4090khassel merged 1 commit intoMagicMirrorOrg:developfrom
khassel merged 1 commit intoMagicMirrorOrg:developfrom
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Replace isPrivateTarget() + fetch() two-step (vulnerable to TOCTOU / DNS rebinding) with resolve-then-pin: DNS is resolved once, the IP is validated, and the validated IP is pinned via an undici Agent dispatcher so fetch() cannot re-resolve to a different address. - Block localhost, non-http protocols and invalid URLs before DNS - Resolve hostname via dns.promises.lookup, reject non-unicast IPs - Pin validated IP in undici Agent lookup callback - Remove isPrivateTarget() (no longer needed) - Update tests to mock dns.promises.lookup and global.fetch
khassel
approved these changes
Apr 4, 2026
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PR #4084 blocked SSRF by checking the IP before
fetch()— butfetch()resolves DNS again on its own. With DNS rebinding (TTL=0, alternating IPs) an attacker can slip a private IP through between check and connection.Fix: resolve DNS once, validate, pin the validated IP for the connection.
No second DNS query → no rebinding window.
isPrivateTarget()is gone, code is shorter than before.Not a likely attack for a typical MagicMirror setup, but it doesn't add complexity so there's no reason not to close the gap.