install: escape control characters in the bun pm untrusted/trust script listing - #38525
install: escape control characters in the bun pm untrusted/trust script listing#38525robobun wants to merge 3 commits into
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…pt listing `bun pm untrusted` and `bun pm trust` print each blocked lifecycle script verbatim. A script containing ESC, CR, C1 or newline bytes could therefore erase or repaint the line it is listed on, so the command the user reviews on screen is not the command that runs once the package is trusted. Add bun_core::fmt::escape_control_chars, a Display adapter that spells out C0 controls, DEL and C1 controls (\x1b, \r, \n, \x7f, \u009b) and leaves everything else untouched, and use it for the script bodies, the package folder name and the resolution in that listing.
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Status: reproduced on 1.4.0 and 1.4.0-canary.1 with a
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WalkthroughChangesControl-character output
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Actionable comments posted: 1
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Inline comments:
In `@test/cli/install/bun-pm.test.ts`:
- Around line 940-996: Expand the test “bun pm untrusted and bun pm trust escape
control characters in dependency scripts” to include newline and tab characters,
plus control characters in dependency resolution and displayed path fields.
Assert both bun pm untrusted and bun pm trust render all affected output fields
escaped, without raw control characters, while preserving the existing success
and script-count assertions.
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src/bun_core/fmt.rssrc/install/lockfile/Package/Scripts.rstest/cli/install/bun-pm.test.ts
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LGTM — focused security hardening that escapes control characters in the bun pm untrusted/trust listing.
What was reviewed:
EscapeControlCharswriter: char range covers C0/DEL/C1;char_indices()+len_utf8()handle multi-byte UTF-8 correctly; defaultwrite_chardelegates towrite_strso nothing bypasses the filter.print_scripts: all three dependency-authored fields (folder path, resolution, script body) wrapped, in bothUntrustedandCompletedbranches; benign output is byte-identical.- Test:
bunEnvsetsNO_COLOR=1, sonot.toContain("\\x1b")won't false-positive on bun's own ANSI codes; pipes drained concurrently; covers ESC, CR, DEL and 8-bit CSI across both commands.
Extended reasoning...
Overview
This PR closes a terminal-escape injection in the bun pm untrusted / bun pm trust script listing — the screen users read before deciding whether to run a dependency's lifecycle scripts. It adds bun_core::fmt::EscapeControlChars, a ~40-line Display/fmt::Write adapter that renders C0 controls, DEL and C1 controls as visible escapes (\\n, \\x1b, \\u009b, …), and routes the folder name, resolution and script body in List::print_scripts through it. A new test in test/cli/install/bun-pm.test.ts installs a file: dependency whose postinstall carries ESC/CR/DEL/U+009B and asserts both commands print the escaped form and no raw control bytes.
Security risks
The change is pure hardening: it adds output escaping to a trust-decision UI, so the risk direction is strictly toward safer. I checked that the escaper cannot be bypassed — it sits between the inner Display and the Formatter as a fmt::Write shim, so anything the wrapped value writes (including Resolution::fmt's own output) is filtered; the default write_char implementation delegates to write_str. Invalid UTF-8 in the raw byte-slice case goes through bstr::BStr, which emits U+FFFD (not a control char). A lone raw 0x9B (invalid UTF-8) therefore renders as � rather than reaching the terminal as CSI. The C1 range is matched on decoded chars, so the 2-byte UTF-8 encoding of U+009B is caught while the adjacent U+00BB (») correctly passes through.
Level of scrutiny
Medium. The fix is security-relevant but the mechanism is simple, additive, and confined to display formatting — no change to install/trust semantics. Output for scripts without control characters is byte-identical (only the matches! branch diverts). No CODEOWNERS coverage on the touched paths.
Other factors
- Both
PrintFormatarms are covered (the PR description's "fix the whole class" applies here — untrusted and completed listings share the vulnerability). - The test's negative assertion
not.toContain("\\x1b")would false-positive if bun emitted its own ANSI color codes, butbunEnvsetsNO_COLOR=1/ clearsFORCE_COLOR, and stdout is piped, sopretty!strips its<cyan>/<d>tags. The test drains stdout/stderr/exited concurrently and usestempDirper harness conventions. - The trusted-step script hides its control-char payload behind
#(a comment in bun's cross-platform shell), so trusting the package only runsecho— the test is hermetic and safe on all platforms. - The escaped form is not strictly injective (a literal 4-char
\\x1bin a script displays the same as an actual ESC byte), but that's acceptable for the threat model: the point is that the malicious prefix stays visible and the terminal cursor cannot move.
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Heads up: #38536 ( |
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I reviewed this PR and didn't find any bugs. Because it hardens security-relevant output (the listing users read before bun pm trust) and adds new public surface in bun_core::fmt, a human look would still be worthwhile. There are also three open comment-cop flags on the new doc comments that should be dismissed or trimmed before merge.
What was reviewed:
EscapeControlCharswrite shim: char-index slicing, C0/DEL/C1 range boundaries (»U+00BB correctly outside),len_utf8advance — no over-read.print_scripts: all three dependency-authored fields (path, resolution, script body) routed through the escaper for bothUntrustedandCompletedformats.- Tests:
bunEnvsetsNO_COLOR=1, so thenot.toContain("\\x1b")assertions can't false-pass on bun's own ANSI codes; second test's Windows skip is justified (NTFS rejects the filenames).
Extended reasoning...
Overview
The PR closes a terminal-spoofing hole in bun pm untrusted / bun pm trust: dependency-authored strings (lifecycle script bodies, the node_modules folder name via alias, and the resolution via file: spec) were printed raw, so an embedded ESC[2K ESC[1G sequence could erase and repaint the listing line, and a newline could forge extra entries. The fix adds bun_core::fmt::EscapeControlChars<T> — a Display-wrapping fmt::Write shim that renders C0 (0x00–0x1F), DEL (0x7F), and C1 (U+0080–U+009F) as \\n/\\r/\\t/\\xNN/\\uNNNN and passes everything else through — plus a &[u8] convenience wrapper over bstr::BStr. List::print_scripts now routes all three fields through it. Two integration tests exercise ESC/CR/LF/TAB/DEL/U+009B in the script body across both commands, and ESC/CR in the path and resolution.
Security risks
This is a security hardening change to output the user reads before granting execution trust. The escaper is additive-only (no validation is loosened), the character-range match is correct at both edges, and non-control multibyte characters like » (U+00BB) fall outside the C1 range and pass through unchanged. Invalid UTF-8 bytes reach the shim as U+FFFD via bstr::BStr's Display, which is not a control character and is left as-is. I did not find a way for a control byte to bypass the filter. The residual risk is scope: other install output that echoes dependency-authored strings (bun pm ls, install summaries, bun info) is explicitly deferred to a follow-up per the PR description — reasonable, but a maintainer should confirm that scoping.
Level of scrutiny
Medium-high. The Rust change is small and mechanically simple (a ~25-line fmt::Write adapter and four call-site wraps), but it sits on a trust boundary and introduces a new public helper in bun_core::fmt that other call sites are expected to adopt. Per the repo's review guidance, new user-facing/public API surface and security-relevant paths warrant a maintainer sign-off rather than auto-approval.
Other factors
- Three unresolved
comment-copbot flags remain on the new doc comments (fmt.rs:3330, fmt.rs:3337, Scripts.rs:430). The section-header banner matches the file's established convention (dozens of identical banners in fmt.rs) and the rustdoc explains the security why, so these read as false positives — but the author should dismiss or trim them rather than merge over open lint comments. - The CodeRabbit request for newline/tab and path/resolution coverage was addressed in e736797 and the thread is resolved.
- Test soundness:
bunEnvsetsNO_COLOR=1(harness.ts:73), so bun's own<d>/<cyan>markup does not emit ESC bytes and thenot.toContain("\\x1b")assertions test only the dependency-authored content. The WindowsskipIfon the second test is correct because the fixture requires creating a directory namedreal\\rpkg, which NTFS rejects.
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Responding to the review round: the extra coverage CodeRabbit asked for landed in e736797 (newline and tab in the script body, plus control characters in the package path and resolution), and 53a0e31 trims the comments comment-cop flagged; the two flags that remain (the section banner this file uses for every formatter, and the three-line rustdoc on the new public type) are answered inline and resolved. No code changes beyond comments since e736797. |
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I reviewed this PR and didn't find any bugs. Because it hardens a security-sensitive flow (the listing users read before bun pm trust runs a package's scripts) and introduces a new public bun_core::fmt helper that #38536 will also adopt, a human look would still be worthwhile.
What was reviewed:
EscapeControlCharswriter: C0/DEL/C1 ranges andstart = i + c.len_utf8()indexing are correct;»(U+00BB) and other non-controls pass through; lone non-UTF-8 bytes become U+FFFD viaBStrand can't reach the terminal as raw controls.- All three attacker-controlled fields in
print_scripts(script body, folder path, resolution) are wrapped, in both the»and✓branches. - The
not.toContain("\\x1b")assertions are safe becausebunEnvsetsNO_COLOR=1, sopretty!emits no ANSI of its own. - One design question worth a human call: bidi override characters (U+202A–U+202E, U+2066–U+2069) can also visually misrepresent the listing but are outside C0/DEL/C1 and pass through unchanged.
Extended reasoning...
Overview
The PR closes a terminal escape-sequence injection in bun pm untrusted / bun pm trust: a dependency's lifecycle script body (and its node_modules folder name and resolution string) were printed byte-for-byte, so a package could embed ESC[2K ESC[1G to erase the line Bun just wrote and repaint it with something innocuous. The fix adds a small Display adapter, bun_core::fmt::EscapeControlChars<T>, that renders C0 controls, DEL and C1 controls as visible escape spellings (\\n, \\x1b, \\u009b, …) and passes everything else through, then routes all three attacker-controlled fields in List::print_scripts through it. Two tests in test/cli/install/bun-pm.test.ts exercise the script body (ESC/CR/LF/TAB/DEL/CSI) and the path + resolution fields.
Security risks
The change is itself a security hardening. I checked the escaper's coverage against what a terminal actually acts on: C0 (0x00–0x1F), DEL (0x7F) and C1 (U+0080–U+009F) are all matched; the char_indices() + len_utf8() slicing is correct for multi-byte input, and the escape_control_chars(&[u8]) entry point goes through BStr, which turns invalid UTF-8 into U+FFFD before it reaches the writer, so a lone 0x9B byte cannot slip through as raw CSI. One residual class the adapter does not cover is Unicode bidi controls (U+202A–U+202E, U+2066–U+2069), which can visually reorder the printed line without being C0/C1; whether to include those is a scope/design call for a maintainer rather than a bug in what's here.
Level of scrutiny
Higher than a typical output-formatting change. bun pm untrusted is the screen users are told to read before granting a package the right to execute arbitrary code, so incomplete escaping directly undermines a trust decision. The new EscapeControlChars helper is also public in bun_core::fmt and (per the thread) is being adopted by #38536 for bun pm view / bun info, so its escape set effectively becomes the project-wide answer to "how do we print untrusted strings" — that's the kind of shared abstraction REVIEW.md asks a maintainer to sign off on.
Other factors
All prior bot feedback appears addressed: CodeRabbit's request for newline/tab and path/resolution coverage landed in e736797, and the comment-cop "paragraph-long comment" flags were followed by 53a0e31 shortening the doc comment to three lines (the remaining flag on line 3334 targets a normal 3-line doc comment and reads as a false positive). The tests use bunEnv (which sets NO_COLOR=1) so the not.toContain("\\x1b") assertions won't collide with Bun's own pretty! coloring. The Windows skip on the second test is justified — the filesystem rejects those filenames, so the precondition can't be created there. Given the security-sensitive surface and the new shared helper, I'm deferring rather than approving.
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On the bidi question (U+202A..U+202E, U+2066..U+2069 passing through): that is deliberate scoping, not an oversight. The escape set here is the bytes every terminal acts on (C0, DEL, C1), which is what lets a package erase or overwrite the line bun printed and replace the command outright. Bidi controls only take effect on the minority of terminals that implement bidi, and they reorder the characters on the line rather than removing any of them, so the real command stays on screen. Since #38536 is adopting the same helper, the escape set now lives in one place; if a maintainer wants bidi controls (or other Unicode format characters) included, it is a one-line addition to the |
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Heads-up on the shared struct EscapeControlCharsWriter<'a, 'f>(&'a mut Formatter<'f>);
impl fmt::Write for EscapeControlCharsWriter<'_, '_> {
fn write_str(&mut self, s: &str) -> fmt::Result {
let bytes = s.as_bytes();
let mut start = 0;
let mut cursor = 0;
// `\` doubles as the quote char so the scan stops at nothing else extra.
while let Some(offset) =
strings::index_of_needs_escape_for_java_script_string(&bytes[cursor..], b'\\')
{
let i = cursor + offset as usize;
let (code_point, len) = match bytes[i] {
byte @ (0x00..=0x1F | 0x7F) => (byte as u32, 1),
0xC2 if matches!(bytes.get(i + 1), Some(0x80..=0x9F)) => (bytes[i + 1] as u32, 2),
byte => {
let char_len = strings::wtf8_byte_sequence_length(byte) as usize;
cursor = (i + char_len).min(bytes.len());
continue;
}
};
self.0.write_str(&s[start..i])?;
match code_point {
0x0A => self.0.write_str("\\n")?,
0x0D => self.0.write_str("\\r")?,
0x09 => self.0.write_str("\\t")?,
0x00..=0x7F => write!(self.0, "\\x{:02x}", code_point)?,
_ => write!(self.0, "\\u{:04x}", code_point)?,
}
start = i + len;
cursor = start;
}
self.0.write_str(&s[start..])
}
} |
2 participants
Problem
bun pm untrusted(and the listingbun pm trustprints after running) writes each blocked lifecycle script to the terminal byte for byte, including control bytes.postinstalliscurl ...|sh ;: <ESC>[2K<ESC>[1G » [postinstall]: node scripts/postinstall.jstherefore shows up on screen as» [postinstall]: node scripts/postinstall.js:ESC[2Kerases the line bun just wrote andESC[1Gmoves back to column 1, so the package repaints its own entry.\r, newlines (forging extra entries), DEL and the 8-bit C1 controls (U+0080..U+009F, e.g. U+009B = CSI) pass through the same way. Reproduced on 1.4.0 and 1.4.0-canary.1, on a pty and on a pipe.bun pm trust, so the command reviewed and the command executed can differ.List::print_scriptsinsrc/install/lockfile/Package/Scripts.rsformats the script body (and the package folder name and resolution, which a dependency also controls through aliases andfile:specs) withBStr, which only replaces invalid UTF-8.Fix
bun_core::fmt::escape_control_chars/EscapeControlChars(src/bun_core/fmt.rs): aDisplayadapter that writes C0 controls, DEL and C1 controls as\n,\r,\t,\x1b,\x7f,\^[and passes every other character (including non-ASCII such as the»bun itself prints) through unchanged. It wraps anyDisplay, so it works on both byte slices and existing formatters likeResolution::fmt.print_scriptsroutes the script body, the folder name and the resolution through it, for both the untrusted (») and completed (✓) formats. Output for scripts without control characters is byte-identical to before.bun pm trustwill run (thecurl ...|shprefix stays visible) and cannot move the cursor, so the listing shows exactly the string that gets executed.test/cli/install/bun-pm.test.ts("bun pm untrusted and bun pm trust escape control characters in dependency scripts"): installs afile:dependency whose postinstall carries ESC, CR, DEL and U+009B, then checks both commands print the escaped text and no raw control characters. Fails on the released binary (raw bytes in stdout), passes with this change; the rest of the file still passes.;: \x1b[2K\x1b[1G » [postinstall]: ...on one line; an alias containing ESC/CR renders as./node_modules/bad\x1b[2Kname\r @pkg.cargo clippy -p bun_core -p bun_install,cargo fmt --check,test/internal/source-lints/clean.Background
preinstall/install/postinstall/...) of dependencies are not run bybun installunless the package is intrustedDependencies.bun pm untrustedlists the blocked scripts so the user can decide;bun pm trust <name>runs them and adds the package totrustedDependencies, then prints the same listing with✓markers.ESC [). In UTF-8 output they are the two-byte sequencesC2 80..C2 9F, which is why the adapter works on decoded characters rather than raw bytes; the multi-byte»(U+00BB,C2 BB) is not a control and is left alone.core::fmt::Writeshim placed between the innerDisplayand the realFormatter, so whatever the inner value writes is filtered;pretty!'s{s}/{f}placeholders are plainDisplayplaceholders, so the call sites only needed their argument wrapped.pm untrusted/pm trustlisting is changed here. Other install output that echoes dependency-authored strings (package names in summaries,bun pm ls,bun info, ...) can adopt the same helper separately.no test proof · iteration 1 · Platform-specific test(s) that do not run on this machine. Deferring to CI, which covers all platforms: test/cli/install/bun-pm.test.ts