tls: apply tls.DEFAULT_CIPHERS to servers and every TLS context built without ciphers by robobun · Pull Request #41810 · oven-sh/bun

robobun · 2026-09-07T05:39:53Z

Problem

tls.DEFAULT_CIPHERS = "..." is a silent no-op for tls.createServer, https.createServer, tls.createSecureContext, Bun.serve and Bun.listen. A server created after the assignment still negotiates the excluded suites (for example ECDHE-RSA-AES256-GCM-SHA384 after tls.DEFAULT_CIPHERS = "ECDHE-RSA-AES128-GCM-SHA256"). Node refuses them with alert 40. Only tls.connect honoured the assignment, because it passes the default explicitly.
The cause: fix(tls) fix ciphers #21545 made SSLConfig.fromJS fall back to the stored default list when no ciphers option is given. The bindgen port (Add new bindings generator; port SSLConfig #23169) dropped that line. RareData::tls_default_ciphers had no native reader left (src/runtime/socket/SSLConfig.rs:251).

Fix

Restore the fallback in SSLConfig::from_generated and tls_true_defaults: with no ciphers option, ssl_ciphers is the list assigned through tls.DEFAULT_CIPHERS. new SecureContext() with no options uses tls_true_defaults instead of SSLConfig::zero(). When nothing was assigned, nothing changes.
A default list with no TLS 1.2 cipher left (only TLS_* names) raises the protocol floor to TLS 1.3, also when maxVersion is lower (then every handshake fails, as with Node's emptied list). BoringSSL keeps its built-in TLS 1.2 list when SSL_CTX_set_cipher_list("") matches nothing, so without the bump TLS 1.2 clients would still get through.
Correct because this is the one place every TLS consumer builds its config from JS options, so the policy reaches all server surfaces at once. is_using_default_ciphers stays true, so the SSL_CTX cache key keeps its meaning. An empty tls: {} still means "no TLS" for Bun.connect/Bun.listen/Bun.serve: the default does not mark the config as non-empty.
Verified: test/js/node/tls/node-tls-server.test.ts ("tls.DEFAULT_CIPHERS applies to servers created without a ciphers option", fails 5 of 8 probes on 1.4.3). Also the rest of test/js/node/tls/, test/js/bun/net/, test/js/node/https/ and 15 test-tls-* node parallel tests.

Background

tls.DEFAULT_CIPHERS is Node's documented process-wide cipher policy. Its setter stores the TLS 1.2 part of the string in RareData (Bun__setTLSDefaultCiphers). TLS 1.3 suite names are stripped because BoringSSL has a fixed TLS 1.3 suite set and SSL_CTX_set_cipher_list only parses the TLS 1.2 grammar.
SSLConfig (src/http/ssl_config.rs) is the owned C-string bag that us_ssl_ctx_from_options turns into an SSL_CTX. from_generated fills it from the bindgen dictionary for Bun.serve, Bun.listen/connect, SecureContext, fetch's tls option and the node:tls paths on top of them.

Notes

Probe matrix with the fix (server built without ciphers, client pinned to one TLS 1.2 suite), tls.createServer / Bun.serve / Bun.listen identical:
- unset: AES256-GCM ok, AES128-GCM ok, RSA-kx AES128-GCM ok, default client TLS 1.3 (same as 1.4.3, no baseline shift)
- ECDHE-RSA-AES128-GCM-SHA256: AES256-GCM alert 40, AES128-GCM ok, RSA-kx alert 40, default client TLS 1.3
- TLS_AES_128_GCM_SHA256: every TLS 1.2 client ERR_SSL_TLSV1_ALERT_PROTOCOL_VERSION, default client TLS 1.3
- TLS_AES_128_GCM_SHA256 plus server maxVersion: "TLSv1.2": every client fails (ERR_SSL_NO_SUPPORTED_VERSIONS_ENABLED on the server side)
Not covered, unchanged: fetch() without a custom TLS context uses the HTTP thread's shared client SSL_CTX, which never read JS-side TLS defaults. The report was about servers.
A first version did this in JS (InternalSecureContext, tls.Server[buntls], _http_server.ts). Self-review pointed at the lost native fallback from fix(tls) fix ciphers #21545 as the right layer, since it also covers Bun.serve/Bun.listen and does not move servers with no assignment onto a different cipher list. Restructured accordingly.
Pre-existing, unrelated failures seen locally on main as well: "SNICallback runs even when the requested servername matches the bind hostname", "tls.Server socket destroySoon > delivers the whole stream when destroySoon follows end", "root certificate initialization > concurrent Workers", two socket.test.ts cases that need internet.
Found while here and handed off separately: tls.createServer({ secureContext }) never serves the context's certificate (ERR_SSL_NO_CERTIFICATE_SET on every handshake).

no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/tls/node-tls-server.test.ts

…hers An SSLConfig built without a `ciphers` option falls back to the list assigned through `tls.DEFAULT_CIPHERS`, in the one native place every TLS consumer goes through (tls.createServer, https.createServer, createSecureContext, Bun.serve, Bun.listen). #21545 added this fallback in SSLConfig.fromJS and the bindgen port (#23169) dropped it, so only tls.connect (which passes the default explicitly) still honoured it. A default list with no TLS 1.2 cipher left raises the protocol floor to TLS 1.3, like Node's configSecureContext.

coderabbitai · 2026-09-07T05:40:00Z

Walkthrough

Changes

The VM now exposes its stored TLS 1.2 default cipher list. SSL configuration applies this list when no explicit cipher option is provided. End-to-end tests cover TLS, HTTPS, and Bun.serve.

TLS default cipher propagation

Layer / File(s)	Summary
Expose and apply VM TLS defaults `src/jsc/VirtualMachine.rs`, `src/runtime/socket/SSLConfig.rs`	`VirtualMachine` exposes its stored default cipher list. SSL configuration applies it when no explicit list exists and raises the minimum TLS version to 1.3 when the list is empty.
Validate server cipher behavior `test/js/node/tls/node-tls-server.test.ts`	The test verifies default cipher behavior for TLS, HTTPS, and `Bun.serve`, including excluded suites, allowed suites, and TLS 1.3-only configuration.

Suggested reviewers: jarred-sumner, cirospaciari

Merge Risk: 🟡 Moderate · up to 4d09a

TLS servers or contexts created with otherwise empty TLS options may ignore tls.DEFAULT_CIPHERS, allowing cipher suites that users intended to disable. The configuration-presence handling should be corrected before merge.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Description check	✅ Passed	The description clearly explains the problem, implementation, affected TLS consumers, behavior changes, and verification results. It does not use the exact template headings, but it includes the requi…
Title check	✅ Passed	The title clearly and concisely describes the main change: applying tls.DEFAULT_CIPHERS to servers and TLS contexts without explicit cipher settings.

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robobun · 2026-09-07T05:40:11Z

^{Updated 11:17 PM PT - Sep 7th, 2026}

❌ @robobun, your commit cff3018 has 2 failures in Build #112446 (All Failures):

test/js/node/test/parallel/test-crypto-dh-leak.js - code 1 on 🐧 13 x64-asan
test/js/bun/http/async-iterator-stream.test.ts - 1 failing in the parallel batch on 🐧 13 aarch64

🧪 To try this PR locally:

bunx bun-pr 41810

That installs a local version of the PR into your bun-41810 executable, so you can run:

bun-41810 --bun

robobun · 2026-09-07T05:43:43Z

Status

Reproduced on 1.4.3 / d316760e8: after tls.DEFAULT_CIPHERS = "ECDHE-RSA-AES128-GCM-SHA256", a TLS 1.2 client pinned to ECDHE-RSA-AES256-GCM-SHA384 still completes the handshake against tls.createServer, https.createServer and Bun.serve built without a ciphers option. Node refuses it with alert 40.

bun bd test test/js/node/tls/node-tls-server.test.ts -t "DEFAULT_CIPHERS applies"
# passes with this branch; USE_SYSTEM_BUN=1 fails 5 of 8 probes

The fix restores the native SSLConfig fallback to the stored default list (lost in the bindgen port of #21545), so every server surface picks it up at once. Self-reviewed: the first draft patched three JS builders; the review pointed at the native layer as the original design, restructured accordingly.

CI on cff3018: the lanes that touch this diff are green. The two red tests are unrelated and fail on other branches too: test/js/node/test/parallel/test-crypto-dh-leak.js (x64-asan RSS threshold, also red on main) and test/js/bun/http/async-iterator-stream.test.ts (plain-HTTP stream test, debian aarch64). Both are reported separately.

claude

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

…s of maxVersion With maxVersion pinned below 1.3 this leaves no version to negotiate, so every handshake fails instead of BoringSSL's built-in TLS 1.2 list staying in effect. Same outcome as Node's emptied TLS 1.2 list, and the same rule the explicit ciphers option already follows in tls.ts.

coderabbitai

Actionable comments posted: 2

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Inline comments:
In `@src/runtime/socket/SSLConfig.rs`:
- Line 256: Update the TLS option handling around apply_default_ciphers so the
any flag is set whenever default ciphers install a value in result.ssl_ciphers,
ensuring the configured cipher list is retained instead of returning None for
otherwise empty options.

In `@test/js/node/tls/node-tls-server.test.ts`:
- Around line 2732-2733: Remove the inline fixture comment near the TLS 1.3-only
setup, leaving the test setup and assertions unchanged.

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Reviewing files that changed from the base of the PR and between ae3c3ad and 4d09a54.

📒 Files selected for processing (3)

src/jsc/VirtualMachine.rs
src/runtime/socket/SSLConfig.rs
test/js/node/tls/node-tls-server.test.ts

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claude

I re-reviewed after 4d09a54 and d1974ce and found no further bugs. The maxVersion fail-open case I flagged is fixed — ssl_min_version is now raised to TLS 1.3 unconditionally when the stored default list is empty, so a maxVersion: "TLSv1.2" context fails closed instead of negotiating BoringSSL's built-in TLS 1.2 list. Since this changes process-wide TLS cipher policy, a human sign-off is still worthwhile.

What was reviewed:

apply_default_ciphers not setting any/requires_custom_request_ctx — every real caller (server needs cert/key, tls: true goes through tls_true_defaults) already has any = true, so the Ok(None) early-return can't drop a dupe_z allocation.
is_using_default_ciphers stays true in the else-branch, so the SSL_CTX cache key semantics are unchanged from the pre-#23169 behavior.
Test spawns with bunExe()/bunEnv, drains pipes concurrently, uses port: 0, asserts stderr/stdout before exitCode.

Extended reasoning...

Overview

This PR restores the tls.DEFAULT_CIPHERS fallback that was dropped during the bindgen port (#23169). It adds a tls_default_ciphers() accessor on VirtualMachine reading from RareData, and an apply_default_ciphers() helper in SSLConfig.rs that copies the stored default into cfg.ssl_ciphers (via dupe_z) when no explicit ciphers option was given. When the stored list is empty (only TLS 1.3 suite names were assigned), it raises ssl_min_version to TLS 1.3 so BoringSSL cannot fall back to its built-in TLS 1.2 list. The helper is wired into both the from_generated else-branch and tls_true_defaults(). A subprocess-spawning test probes tls.createServer, https.createServer, and Bun.serve to verify excluded suites are refused and a TLS-1.3-only default raises the protocol floor.

Security risks

This is a TLS cipher-policy change. The direction is strictly fail-closed: previously tls.DEFAULT_CIPHERS was silently ignored for servers (permitting suites the operator intended to exclude); now the assignment is enforced. My earlier review caught a fail-open edge: gating the TLS 1.3 floor bump on ssl_max_version >= tls1_3 meant a maxVersion: "TLSv1.2" context with a TLS-1.3-only default would still negotiate every built-in TLS 1.2 suite. Commit 4d09a54 removed that guard — the floor is now raised unconditionally, and a min>max conflict fails the handshake rather than silently widening the cipher set. The state is per-VM (RareData), not a process global, so workers are isolated correctly.

Level of scrutiny

High — REVIEW.md explicitly calls out TLS/crypto paths as requiring that security checks fail closed and that flags not be removed without understanding them. The change is small and mirrors both Node's configSecureContext and the pre-#23169 Bun behavior, but process-wide cipher policy is exactly the kind of change that warrants a human maintainer's eyes before merge. I'm not approving on that basis alone.

Other factors

The candidate leak (apply_default_ciphers allocates via dupe_z but doesn't set any, so from_generated could return Ok(None) and drop the allocation) was investigated: the any fold at lines 195-220 and 261-264 is true for any config that has cert/key/ca (required for servers) or reject_unauthorized explicitly set, and the bare tls: true shorthand goes through tls_true_defaults() which always returns the config. is_using_default_ciphers is intentionally left true so the SSL_CTX cache key retains its pre-regression meaning (the PR description calls this out). The test follows CLAUDE.md conventions: bunExe()/bunEnv, port: 0, concurrent pipe drain, stderr/stdout asserted before exitCode, no external network, and covers the sibling entry points (tls/https/Bun.serve) plus the TLS-1.3-only floor case. Commit d1974ce only shortened doc comments.

claude

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

…RS; run the test probes concurrently

claude

Code review found no issues

No high-confidence issues detected in this change.

Still open from earlier reviews (1):

Unresolved: 1 minor or pre-existing.

claude

Code review found no issues

No high-confidence issues detected in this change.

Jarred-Sumner · 2026-10-06T06:21:41Z

Superseded by #44618, which consolidates the open TLS pull requests. This fix and its tests are in there, either as written, rewritten smaller, or merged with the other PRs that patched the same cause (see the "By area" list in that PR). Closing in favor of it.

…rs (#41810) tls.connect() honoured an assignment: tls/https servers, Bun.serve, Bun.listen and Bun.connect kept BoringSSL's list. SSLConfig applies it again wherever no `ciphers` option is given. A list of TLS 1.3 suites only is stored as an empty TLS 1.2 list, which BoringSSL reads as "keep the built-in one", so it raises the minimum version to TLS 1.3, as in Node. Nothing changes until tls.DEFAULT_CIPHERS is assigned.

…lving `..` as text (#40984) Path::join normalises, so "linkdir/../key.pem" with linkdir a symlink named another file than the one the kernel opens, for absolute paths too, which needed no pinning at all. On POSIX an absolute path is now kept as typed and a relative one is appended to the cwd of the call. Windows keeps join: Win32 resolves `..` the same way, and join knows `C:foo` and `\foo`. append drops a trailing slash, with which no file opens, so such a path is refused as it was. Also covers `tls: true` in the tls.DEFAULT_CIPHERS test (#41810).

…1810) apply_default_ciphers filled ssl_ciphers, and raised the minimum version for a list of TLS 1.3 suites only, without setting requires_custom_request_ctx. fetch and WebSocket look at that flag alone, so tls: { rejectUnauthorized: false } kept the default context and its ciphers while tls: { ca } followed the assignment. The fallback sets the flag, like an explicit `ciphers`. It is applied once `any` is decided, so tls: {} still means no TLS configuration. While nothing is assigned it returns before it writes anything.

The default context of fetch is built on the HTTP thread from fixed options, so a fetch with no `tls`, or with tls: {}, ignored an assignment that tls.connect, https.get and, in Node, fetch itself follow. Such a request now takes the config of `tls: true`. One Option check while nothing is assigned.

…ssigned (#41810) The HTTP/3 client has one context, so it refuses a request whose config needs its own, as it does for an explicit `ciphers` option. Pins that as a known limit.

new WebSocket("wss://...") without a tls option and RedisClient tls: true share one SSL_CTX that the VM built once from fixed options and kept for its lifetime, so they ignored the assignment. An assignment now drops it, and the next connection builds it from the config of `tls: true`. Open connections hold their own reference. While nothing is assigned it is the same single context. That context cannot fail to build, so the setter lets BoringSSL check the list: "!aNULL" passed the JS check and now throws ERR_SSL_NO_CIPHER_MATCH, as a name that does not exist already did.

The three requests S3Client builds (simple, list, streaming download) carry no TLS config, so they used the default context of the HTTP thread, like fetch without a tls option did. They take the same config, through one helper that fetch now uses too. One Option check while nothing is assigned.

#41810) It warms a socket of the default context, with the default ciphers. After an assignment no request takes a socket from that context, so the handshake only negotiated a suite the list may exclude.

…rs (#41810) tls.connect() honoured an assignment: tls/https servers, Bun.serve, Bun.listen and Bun.connect kept BoringSSL's list. SSLConfig applies it again wherever no `ciphers` option is given. A list of TLS 1.3 suites only is stored as an empty TLS 1.2 list, which BoringSSL reads as "keep the built-in one", so it raises the minimum version to TLS 1.3, as in Node. Nothing changes until tls.DEFAULT_CIPHERS is assigned.

…lving `..` as text (#40984) Path::join normalises, so "linkdir/../key.pem" with linkdir a symlink named another file than the one the kernel opens, for absolute paths too, which needed no pinning at all. On POSIX an absolute path is now kept as typed and a relative one is appended to the cwd of the call. Windows keeps join: Win32 resolves `..` the same way, and join knows `C:foo` and `\foo`. append drops a trailing slash, with which no file opens, so such a path is refused as it was. Also covers `tls: true` in the tls.DEFAULT_CIPHERS test (#41810).

…1810) apply_default_ciphers filled ssl_ciphers, and raised the minimum version for a list of TLS 1.3 suites only, without setting requires_custom_request_ctx. fetch and WebSocket look at that flag alone, so tls: { rejectUnauthorized: false } kept the default context and its ciphers while tls: { ca } followed the assignment. The fallback sets the flag, like an explicit `ciphers`. It is applied once `any` is decided, so tls: {} still means no TLS configuration. While nothing is assigned it returns before it writes anything.

The default context of fetch is built on the HTTP thread from fixed options, so a fetch with no `tls`, or with tls: {}, ignored an assignment that tls.connect, https.get and, in Node, fetch itself follow. Such a request now takes the config of `tls: true`. One Option check while nothing is assigned.

…ssigned (#41810) The HTTP/3 client has one context, so it refuses a request whose config needs its own, as it does for an explicit `ciphers` option. Pins that as a known limit.

new WebSocket("wss://...") without a tls option and RedisClient tls: true share one SSL_CTX that the VM built once from fixed options and kept for its lifetime, so they ignored the assignment. An assignment now drops it, and the next connection builds it from the config of `tls: true`. Open connections hold their own reference. While nothing is assigned it is the same single context. That context cannot fail to build, so the setter lets BoringSSL check the list: "!aNULL" passed the JS check and now throws ERR_SSL_NO_CIPHER_MATCH, as a name that does not exist already did.

…41810) Without a tls option, start_proxy_tls_handshake built the connection to the origin from SSLConfig::default(), so new WebSocket("wss://...", { proxy }) negotiated a suite that the assigned list excludes, while the same URL without a proxy, or with any tls option, followed it. bun_http_jsc sits below bun_runtime and cannot call tls_true_defaults, so what an assigned list does to a config moves to SSLConfig::set_default_ciphers in bun_http, and both callers use it. One Option check while nothing is assigned. The multi-client test moves to a fixture and gains fetch and WebSocket through an http and an https proxy, and Bun.SQL postgres and mysql.