http: fix use-after-free in proxy-tunnel close dispatch - #31952
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A heap-use-after-free in ProxyTunnel::on_close (src/http/ProxyTunnel.rs): when a proxied-TLS response completes inside the data callback that SSLWrapper::handle_reading delivers right before its close callback, the completion frees the HTTPClient, then the close callback in the same read dispatch dereferences the freed client. handle_reading's guard at uws:1017 only checks SSLWrapper state, not client liveness. The completion teardown (close_proxy_tunnel -> ProxyTunnel::shutdown) now marks the connection close-notified, so the pending handle_reading close callback self-bails instead of running on_close on the freed client. The error teardown (close_raw) is untouched: it still relies on on_close -> close_and_fail to deliver the error, so its close callback fires as before. SSLWrapper::shutdown is unchanged, so other shutdown(true) callers are unaffected. Triggers when a proxied https response's final bytes and TLS close_notify arrive in one read (SSL_read returns body, then ZERO_RETURN, in one handle_reading).
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WalkthroughThis PR fixes a heap-use-after-free bug in proxied TLS handling by marking close notification in ChangesProxied TLS UAF Fix
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cirospaciari
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Jun 17, 2026
…letes mid-read (#31959) [publish images] Fixes a use-after-free in the HTTP client's proxy tunnel close path (Sentry BUN-2VY8, ~10 events/day on Windows release builds; reproduces deterministically under ASAN on all platforms). ## Repro `fetch()` through an HTTP CONNECT proxy to an HTTPS origin, where the origin's final response bytes and its TLS `close_notify` reach the client in a single TCP batch (origin writes the response and immediately closes). The regression test builds exactly that: a local CONNECT proxy that holds origin-to-client bytes after the handshake and flushes session tickets + response + close_notify in one write. On an unfixed ASAN build: ``` ERROR: AddressSanitizer: heap-use-after-free READ of size 8 thread T11 (HTTP Client) #0 Option<RefPtr<ProxyTunnel>>::as_ref #1 bun_http::proxy_tunnel::on_close src/http/ProxyTunnel.rs:525 #2 SSLWrapper<*mut HTTPClient>::trigger_close_callback src/uws/lib.rs:802 #3 SSLWrapper<*mut HTTPClient>::handle_reading src/uws/lib.rs:1022 #4 SSLWrapper<*mut HTTPClient>::handle_traffic #5 SSLWrapper<*mut HTTPClient>::receive_data #6 ProxyTunnel::receive src/http/ProxyTunnel.rs:751 freed by: AsyncHTTP::on_async_http_callback_raw src/http/AsyncHTTP.rs:813 HTTPClient::send_progress_update_without_stage_check src/http/lib.rs:3793 ``` ## Cause 1. `handle_reading` processes the batch: `SSL_read` returns the body bytes, the next `SSL_read` hits `close_notify` (`SSL_ERROR_ZERO_RETURN`), which sets `received_ssl_shutdown` and `sent_ssl_shutdown` before flushing the already-decrypted bytes through the data callback. 2. The data callback completes the response. The done path runs `close_proxy_tunnel(true)` -> `ProxyTunnel::shutdown()` -> `SSLWrapper::shutdown(true)`, which hits the already-shut-down early return (`sent_ssl_shutdown || fatal_error`) and returns **without setting `closed_notified`**. The result callback then frees the `ThreadlocalAsyncHTTP` embedding the `HTTPClient`, the exact pointer stored in the wrapper's `handlers.ctx`. 3. Control returns to `handle_reading`. Its liveness guard (`ssl.is_none() || closed_notified()`) passes because neither is set, so `trigger_close_callback()` invokes `on_close(handlers.ctx)` on the freed client. When the allocation has been recycled, `on_close` can ref or close a different request's tunnel instead of faulting. ## Fix `src/uws/lib.rs`: when `SSLWrapper::shutdown(fast_shutdown=true)` takes the already-shut-down early return, fire `trigger_close_callback()` (idempotent via `closed_notified`) so the wrapper is marked closed before the owner detaches and frees `handlers.ctx`. A fast shutdown is a full teardown, and the normal fast-shutdown path already fires the close callback unconditionally; this only closes the gap where the SSL-level shutdown had already happened. Graceful `shutdown(false)` (node:tls half-close via UpgradedDuplex / WindowsNamedPipe) is unchanged, so reads after a sent `close_notify` keep working. ## Verification New test in `test/js/bun/http/proxy.test.ts` (`test.skipIf(!isASAN)`, the UAF is only deterministic under ASAN): fails on an unfixed ASAN debug build with the heap-use-after-free above, passes with the fix. Full `proxy.test.ts` (46 tests) plus `node-tls-connect`, `node-tls-upgrade`, `node-tls-duplex-close-throw-uaf`, `node-tls-socket-allow-half-open-option`, `node-tls-server`, `fetch-tls-cert`, and `node-https-checkServerIdentity` suites pass. ## Note on the asan-lane CI failure (#32144) The intermittent LeakSanitizer failure on the x64-asan shard (deferred napi finalizers parked on a never-drained cleanup-hook list at `bun test` exit) is being fixed in #32146, which carries the same `global_exit()` drain plus a hooks-only guard that skips pending `napi_wrap` finalizers on undrained-loop exits. A subset version of that fix was briefly on this branch (e59bc1d) but without the hooks-only guard it made `test/js/third_party/duckdb/duckdb-basic-usage.test.ts` SEGV at exit on the asan lane (build 62135), exactly the failure mode #32146's guard prevents, so it was reverted (61f9e70). This PR is scoped to the proxy-tunnel UAF; its asan lane can still intermittently hit the pre-existing #32144 leak until #32146 lands. ## Related PRs - #30606 addresses the same crash signature but patches only the `.zig` reference files, which are no longer compiled; this PR fixes the shipping Rust implementation. - #31952 fixes the same UAF by calling a new `mark_close_notified()` helper from `ProxyTunnel::shutdown` (silently setting the flag at one call site, with `close_raw` exempted). This PR instead closes the gap inside `SSLWrapper::shutdown(true)` itself, so every fast-shutdown caller (`ProxyTunnel::shutdown`, `ProxyTunnel::close_raw`, `UpgradedDuplex::close`, `WebSocketProxyTunnel::shutdown`) gets the same "no callbacks after teardown" guarantee without new wrapper API or a shutdown/close_raw asymmetry. The close callback is fired rather than suppressed, so the error teardown path keeps delivering `on_close` -> `close_and_fail` exactly once (idempotent via `closed_notified`). Test here is a deterministic single-shot repro (the test proxy reassembles TLS records and flushes tickets + response + close_notify in one write) rather than an iteration loop. --------- Co-authored-by: Ciro Spaciari MacBook <ciro@anthropic.com>
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Thanks for tracking this down, and for the fixture. This use-after-free was fixed on main by #31959 (merged June 17, I ran this PR's Closing since main already has the fix. If you still see this on a current canary, please open an issue and we will take another look. |
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What this does
fetch()through an HTTP CONNECT proxy tohttps://heap-use-after-frees when a response's final bytes and the TLSclose_notifyland in one read: the response completes, freeing theHTTPClient, then a same-dispatch close callback reads it.Fix: the proxy completion teardown marks the connection close-notified, so the pending close callback self-bails. The error teardown and
SSLWrapper::shutdownare unchanged.Verification
Red/green: unpatched aborts (ASan UAF), patched completes.
close_notifyin one readReview map
ProxyTunnel.rs:ProxyTunnel::shutdownmarks close-notified;close_rawuntoucheduws/lib.rs:mark_close_notifiedhelper*-close-uaf.test.ts: asserts tunnel traversal + exact split