fix(wasm): close DNS-rebinding TOCTOU in the plugin HTTP client#100
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ndreno wants to merge 1 commit into
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fix(wasm): close DNS-rebinding TOCTOU in the plugin HTTP client#100ndreno wants to merge 1 commit into
ndreno wants to merge 1 commit into
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The SSRF guard resolves the target host and checks the IPs, but reqwest re-resolves DNS when it actually connects. A hostile resolver can answer with a public IP for the pre-flight check and then rebind to an internal address for the connection (TOCTOU), bypassing the guard. Install a custom reqwest DNS resolver (GuardedResolver) that resolves and filters internal/loopback/link-local/metadata addresses in one step, on both the default and TLS clients. reqwest connects to exactly the vetted addresses it returns and does not resolve again, so the address that is checked is the address that is connected to. When egress is disallowed and every resolved address is internal, resolution fails (blocked). The per-request pre-flight ssrf_guard is kept for early, clear errors and literal-IP targets. Addresses AR (DNS-rebinding residual) in private #9.
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What
The SSRF guard resolves the target host and checks the IPs, but reqwest re-resolves DNS when it connects. A hostile resolver can return a public IP for the pre-flight check, then rebind to an internal address for the actual connection (TOCTOU) — bypassing the guard.
Fix
Install a custom reqwest DNS resolver (
GuardedResolver) on both the default and TLS clients. It resolves and filters internal / loopback / link-local / cloud-metadata addresses in one step. reqwest connects to exactly the addresses it returns and does not resolve again, so the address that is checked is the address that is connected to. When egress is disallowed and every resolved address is internal, resolution fails (blocked).The per-request pre-flight
ssrf_guardis kept for early, clear errors and literal-IP targets; the resolver is the TOCTOU-safe enforcement point.Scope
Closes the AR (DNS-rebinding residual) item in private #9. With it, #9's other items (DP-4/5/8) having landed in #97, #9 should be fully addressed.
Tests