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…oaded it
The error printer builds a code-frame excerpt for the top stack frame. For a
frame parsed out of an `error.stack` string, it read the frame's source URL
from disk with the module fetcher and printed the file contents.
The running code chooses that source URL. A `//# sourceURL` directive, or a
node:vm `filename`, sets it. So code run through node:vm could name any path
and make the host print that file:
vm.runInNewContext(
'throw new Error("x")\n//# sourceURL=/etc/hostname',
{}, { filename: "sandbox.js" });
The contents of `/etc/hostname` then appear in `console.error`, the uncaught
and unhandled-rejection printers, `Bun.inspect`, and the default Bun.serve 500
body. A whole file is read for a six-line excerpt, so a large named file drives
RSS to the file size. A name with an interior NUL byte aborts the printer on a
debug or ASan build.
Only read the source from disk when the module loader loaded that URL. The
stack-string branch now checks the source-map table, which records a path only
when the loader transpiles it. The other branch already resolves through that
table. A real module still shows its original source. An attacker-named path
shows no excerpt.
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Updated 12:51 AM PT - Sep 6th, 2026
❌ @robobun, your commit 6cfd410 has 2 failures in
🧪 To try this PR locally: bunx bun-pr 41477That installs a local version of the PR into your bun-41477 --bun |
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Included review availability: Your plan provides up to 10 included reviews per hour; 7 remain after this review. WalkthroughThe VM now tracks trusted source-map paths before reading source for remapped stack frames. New subprocess tests cover attacker-controlled paths, interior NULs, caught and uncaught errors, and valid loaded modules. ChangesSource URL disclosure guard
Suggested reviewers: Merge Risk: ⚪ Minimal · up to This change prevents stack-trace source previews from reading attacker-chosen paths while preserving code frames for trusted loaded and embedded sources. Coverage includes the affected VM error-reporting paths, with no current merge-blocking risk identified. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Actionable comments posted: 3
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Inline comments:
In `@src/jsc/SavedSourceMap.rs`:
- Line 263: Update the path-validation logic around SavedSourceMap’s
contains_key check so a hash match alone cannot authorize a disk read. Retain or
look up the complete loaded path and compare it with the requested path before
returning success, while preserving the existing rejection behavior for
non-matching paths.
In `@test/js/node/vm/vm-sourceUrl.test.ts`:
- Around line 75-76: Extend the vm.runInNewContext test fixture around the
existing sourceURL variants with a separate case that omits the sourceURL
directive and passes target as the filename option, including the interior-NUL
target case. Preserve the current sourceURL coverage and expected error-handling
behavior.
- Line 96: Update the exit-code assertion in the vm-sourceUrl test to require
the expected uncaught-error status rather than merely rejecting 134. Keep the
existing output assertions and ensure the check rejects both successful exits
and unrelated native crash statuses.
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The source-map table keys on a wyhash of the path. A membership test on the hash alone accepts any string that collides with a loaded module. The fetch normalizes `..` segments, so a colliding string can still name a real file. Keep the loaded paths by bytes and compare against those. Also cover the node:vm `filename` option in the tests, and require the exact exit code for the uncaught case.
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Inline comments:
In `@test/js/node/vm/vm-sourceUrl.test.ts`:
- Line 71: Update the subprocess fixture in vm-sourceUrl.test.ts to use an .mjs
file with a static `import * as vm from "node:vm"` instead of the generated
CommonJS `require` form, and update the spawned filename to match the new
fixture name.
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…d embedded files The gate on the stack-string branch compared the frame URL against the paths the loader registered. Two URLs the loader itself produces were missing from that set. A frame remapped through an external source map names the map's original source. A frame in a `bun build --compile` executable names an embedded file. Both lost their code frame once `error.stack` had been read. Record each URL the remap emits as trusted when it is emitted. Accept a path the standalone module graph serves, since that is not the filesystem. Cover all three loaded cases on the stack-string path in the tests.
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I re-reviewed after the latest push and found no new issues — all four of my earlier inline comments look addressed (is_embedded_module covers the standalone-graph case, remapped_source_url→trust_path covers external-map sources[] paths, the no-regression tests now touch .stack before console.error so they exercise the already_remapped gate, and every spawn drains stdout/stderr/exited concurrently). Since this is a security fix gating disk reads on an attacker-controllable path, a maintainer sign-off is still warranted.
What was reviewed:
- Traced
allow_source_from_disk: only thealready_remapped(stack-string) branch is gated; live-frame paths are unchanged, so no regression for ordinary uncaught errors. - Checked
trust_pathcan only record URLs emitted bydisplay_source_url_if_neededon a lookup the loader itself resolved — vm/eval code can't reach it to whitelist an arbitrary path. pathsset is accessed only underlock()/unlock();swap_removemirrors the onemap.removeeviction site.- New tests: 8-case leak matrix asserts canary absent + correct exit code; three positive tests (source, external-map bundle,
--compile) now hit the gated branch.
Extended reasoning...
Overview
This PR closes an arbitrary-file-disclosure vector in the error printer: a //# sourceURL directive or node:vm filename could name any on-disk path, and remap_zig_exception would fetch_without_on_load_plugins it to build the code-frame excerpt. The fix adds a byte-keyed paths set to SavedSourceMap tracking every URL the loader itself produced (registered modules, plus original-source URLs emitted by a loaded module's own source-map remap via the new remapped_source_url→trust_path path), and gates the disk read on is_loaded_path || is_embedded_module for frames that were parsed back out of an error.stack string. Live JSC frames (which carry a SourceProvider) are untouched.
Security risks
The change is itself a security hardening. The residual questions are (a) whether the gate can be bypassed — I did not find a route for vm/eval code to reach trust_path, since it is only invoked on display_source_url_if_needed output for a lookup that resolve_source_mapping returned, and that table is populated only by the module loader; and (b) whether the gate over-blocks — the three positive tests (run-from-source, external-sourcemap bundle, --compile binary) now exercise the already_remapped == true branch by touching .stack before console.error, so they would fail if the gate rejected legitimate paths. The PR description already flags the known residual (a sourceURL colliding with a path the app itself loaded excerpts that module's own source) as an acknowledged follow-up.
Level of scrutiny
High — this gates a disk read on attacker-chosen input and touches the error printer used by console.error, uncaught/unhandled printers, Bun.inspect, and the default Bun.serve 500 body. Per the approval guidelines and REVIEW.md ("security checks fail closed and cover every route to the protected effect"), a maintainer should confirm the trust boundary and the acknowledged follow-ups rather than this landing on a bot approval alone.
Other factors
All four of my prior inline findings were addressed by commits 1e0d693/073e85c1/7fcbb2cb: the standalone-module-graph fallback is now checked via is_embedded_module; external-map sources[] paths are recorded via trust_path at all three display_source_url_if_needed call sites; the no-regression fixtures now catch, materialize .stack, and re-print so they actually hit the gate; and the run helper drains all three streams. The paths set additions bracket lock()/unlock() consistently with the existing map accesses. No outstanding third-party CHANGES_REQUESTED reviews are visible in the timeline.
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Status: ready for review. Reproduced on stock bun 1.4.3: a The fix gates the disk read on the frame's URL being one the loader produced. Details are in the PR body. CI: |
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Pre-merge verification on current main. I built the test merge of this branch (6cfd410) onto main (367d939), and a second build whose The matrix is 510 cells, one child process per cell, one private directory tree per cell. It covers 7 code-entry doors (
Cell by cell, main against this PR: 160 cells change and 350 are byte identical (stdout, stderr, exit code, and open count). Every changed cell moves in one direction. 120 go from "prints the named file" to "prints no excerpt". 40 go from SIGABRT to an ordinary exit. No cell changes in any other way. After the fix the release build and the debug build give the same answer on all 510 cells. The two legitimate controls are byte identical before and after. A module run from source still shows its own source line. A bundled module with an external source map still shows the original One detail the release column adds. The 40 interior-NUL cells abort on a debug or ASAN build. On release they do not abort. They read the file with the name truncated at the NUL and print its contents. The assert masks a disclosure instead of preventing one, so the release number for main is 160, not 120. Residual, unchanged by this PR and already named in the body: a Suites run against the PR build, all with no failures: this PR's own test file (14 pass, on both profiles), Two notes for whoever merges this:
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Problem
//# sourceURL, or anode:vmfilename), so code innode:vmcan name any path and make the host print that file.remap_zig_exception(src/jsc/VirtualMachine.rs) callsfetch_without_on_load_plugins(PrintSource)on the URL. The contents reachconsole.error, the uncaught printer,Bun.inspect, and the defaultBun.serve500 body. The read is whole-file. An interior NUL aborts a debug or ASan build.Fix
error.stackstring (remapped == true, the pathnode:vmandevalerrors take) are attacker-chosen. Live frames are unchanged.SavedSourceMapkeeps every registered path by bytes (paths). A hash-only check is not enough: the fetch normalizes.., so a colliding string could still name a real file.remapped_source_urlrecords it viatrust_path), and a file embedded in abun build --compileexecutable (is_embedded_module).test/js/node/vm/vm-sourceUrl.test.ts. Eight leak cases fail on stock bun. Three loaded-module cases (source, external map, compiled) take the stack-string path and keep their excerpt. Also the vm, inspect-error, stack, and bundler_compile suites.Background
ZigExceptionframes come from live JSC frames, which keep the source in memory, or from theerror.stackstring when only that is left. The parsed form has no source, so the printer re-read the file the frame names.SavedSourceMapmaps a module path to its source map. The loader inserts an entry when it transpiles a module or loads one with a//# sourceMappingURL.Notes
node:vmerror reachesremap_zig_exceptionwithframes[top].remapped == true, so it took the stack-string branch that fetched unconditionally.node:vmcode run under a realfilename(vm.runInThisContext,vm.Script, the jest and vitest runtime shape) had a code frame read from that file. It now has none on this path, since the loader never loaded the file. Thefilenamerows of the test matrix assert this. The frame line and column are unchanged. Node prints the in-memory line for this case, so neither the old nor the new output matches it.sourceURLandfilename, caught and uncaught, with and without an interior NUL.//# sourceURLthat collides with a path the app itself loaded still excerpts that module's file, not the code that ran. This discloses only the app's own source.SourceProviderit already holds. That restores thevmfilenameexcerpt with the text that ran, fixes the collision case, and matches Node. The string-parsed frame has no provider handle today, so it is not a cheap addition to this gate.vmfilenamecost above.BUN_DISABLE_SOURCE_CODE_PREVIEWstill suppresses the excerpt entirely, unaffected.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/vm/vm-sourceUrl.test.ts