Stop .preflight lines escaping to other binaries

[vertti]

A .preflight file could execute an arbitrary binary, contradicting the documented contract that every line runs preflight.

The mismatch

Two checks disagreed about what "already prefixed" means:

Location	Test
preflightfile.go:75	strings.HasPrefix(trimmed, "preflight") → don't prepend
cmd_run.go:56	parts[0] == "preflight" → substitute the real binary

A token that starts with preflight but isn't equal to it satisfies the first and escapes the second. And because the token contains a slash, exec.Command skips $PATH and runs it relative to the working directory:

.preflight:
    env HOME
    preflight/../evil.sh

$ preflight run
[OK] env: HOME
PWNED: arbitrary code executed

FindFile discovers .preflight by walking up from the working directory, so git clone && cd repo && preflight run — or a CI step that does the same — is remote code execution from repo content.

Fix

• ParseFile compares the first token rather than the prefix, so preflight/../evil.sh becomes preflight preflight/../evil.sh and resolves as an unknown subcommand.
• cmd_run substitutes the resolved preflight binary unconditionally. ParseFile now guarantees the token, so this always fired anyway — making it unconditional means a future parser change can't turn a line back into a path to some other program.

After: exit=1, and PWNED never appears. Normal files (comments, bare commands, explicitly-prefixed lines) are unchanged.

Tests

Table written first, confirmed red on the escape cases: paths starting with preflight, lookalike tokens like preflightfoo, and absolute/relative paths all now get prefixed rather than executed.

Related, not fixed here

The residual error from the exploit is unknown command "echo", not unknown command "preflight/../evil.sh" — because transformArgsForHashbang saw an existing file as the first argument and rewrote the invocation to run --file, then parsed the payload script as a preflight file. Harmless now that lines can only invoke preflight, but it confirms the separate finding that any existing file passed as the first argument is treated as a preflight script, with no executable-bit or shebang check. That's the knownSubcommands issue — next PR.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: d68c3093-5eab-4d9f-b27d-9739fba28b10

📥 Commits

Reviewing files that changed from the base of the PR and between b9cdca9 and 63ebb50.

📒 Files selected for processing (3)

• cmd/preflight/cmd_run.go
• pkg/preflightfile/preflightfile.go
• pkg/preflightfile/preflightfile_test.go

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.24%. Comparing base (b9cdca9) to head (63ebb50).

Files with missing lines	Patch %	Lines
cmd/preflight/cmd_run.go	0.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (50.00%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #220      +/-   ##
==========================================
+ Coverage   93.19%   93.24%   +0.04%     
==========================================
  Files          50       50              
  Lines        1865     1864       -1     
==========================================
  Hits         1738     1738              
+ Misses         92       91       -1     
  Partials       35       35              

Files with missing lines	Coverage Δ
pkg/preflightfile/preflightfile.go	90.24% <100.00%> (ø)
cmd/preflight/cmd_run.go	25.00% <0.00%> (+0.75%)	⬆️

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