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fix(task): refuse a UNC working directory the cmd shell cannot use - #12066
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Included review availability: Your plan includes up to 10 reviews per rolling hour; 9 remain after this review. 📝 WalkthroughWalkthroughWindows task execution now rejects ChangesUNC cmd.exe guard
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to This change prevents tasks from silently running in the wrong directory for unsupported UNC working paths; no actionable merge-blocking risk remains beyond normal checks and review. Possibly related PRs
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Greptile SummaryThe PR prevents Windows tasks and cache command inputs from running under cmd.exe in an unintended directory when their requested working directory is a UNC path.
Confidence Score: 5/5The PR appears safe to merge. No blocking failure remains. Important Files Changed
Reviews (3): Last reviewed commit: "fix(task): refuse a UNC working director..." | Re-trigger Greptile |
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Inline comments:
In `@src/task/task_executor.rs`:
- Around line 1718-1721: Centralize the Windows working-directory validation by
invoking cmd_shell_cannot_use_dir before current_dir() in both exec_program and
resolve_cache_command_inputs, including the CmdLineRunner path used for cached
command_inputs. Add a regression test covering a UNC task directory with
cache.command_inputs and verify the command is rejected before spawning cmd.exe.
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e2e-win/task_unc_dir.Tests.ps1src/file.rssrc/task/task_executor.rs
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cmd.exe does not accept a UNC path as its working directory. It says so on
stderr, starts in C:\Windows instead, and carries on — so on Windows a mise task
in a project on a UNC share runs somewhere the user never asked for, and mise
reports success.
Measured on 2026.8.6 windows-x64 with the project at
\\wsl.localhost\<distro>\home\...\proj and an isolated MISE_* environment:
run = "cd" -> prints C:\Windows, exit 0
run = "...$PWD.Path", shell = "pwsh -c" -> prints the UNC project dir, exit 0
run = "echo %MISE_PROJECT_ROOT%" -> prints the UNC path
run = "echo hello> made-by-task.txt" -> Access is denied, file never created
The third row is the sharpest: the task's environment says the project root is
the UNC path while its working directory is C:\Windows. The fourth is the
reachable harm — a relative write lands in C:\Windows, fails on permissions, and
nothing tells the user the directory moved. Where the process can write, it
writes to the wrong place and the task passes.
Two call sites set that working directory, and both are refused:
- exec_program, which spawns the task itself. Skipped under --dry-run, where
nothing is spawned and a preview has no reason to fail.
- resolve_cache_command_inputs, which runs cache.command_inputs through the
same inline shell. This one matters more, because those commands feed the
artifact cache key: measured on a UNC share, an input reading a file that
exists in the project fails, while the same config on a local path succeeds.
Reuses the two predicates that already exist: path::is_cmd_shell_program, which
knows cmd/cmd.exe/CMD.EXE and full paths, and file::is_unc_path, which already
matches both Prefix::UNC and Prefix::VerbatimUNC.
Not keyed off the existing cmd_verbatim flag: that is only set for inline
scripts, so a file task reaching cmd.exe through windows_default_file_shell_args
would slip past it.
Config discovery, mise trust and mise env were measured on the same UNC tree and
are unaffected.
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cmd.exedoes not accept a UNC path as its working directory. It says so on stderr, starts inC:\Windowsinstead, and carries on. Sincecmd /cis mise's default inline shell on Windows, atask in a project on a UNC share runs somewhere the user never asked for, and mise reports
success.
What happens
Project at
\\wsl.localhost\Ubuntu-Preview\home\jam\unctest\proj, isolatedMISE_*,2026.8.6 windows-x64:
mise passes cmd's warning through and ignores it. Exit code 0.
run = "cd"— defaultcmd /cC:\Windows, exit 0run = "Write-Output $PWD.Path",shell = "pwsh -c"run = "echo ROOT=%MISE_PROJECT_ROOT%"run = "echo hello> made-by-task.txt"Access is denied., exit 1, file never createdThe third row is the sharpest: the task's environment says the project root is the UNC path
while its working directory is
C:\Windows. The fourth is the reachable harm — a relative writelands in
C:\Windows, fails on permissions, and nothing connects "Access is denied" to a workingdirectory that moved. Where the process can write, it writes to the wrong place and the task
passes.
Measured as unaffected on the same UNC tree: config discovery across three levels,
mise trust,mise env, andpwshtasks, which run in the right directory.The change
Refuse before spawning, and name the shells that do accept a UNC working directory:
Both predicates already existed and are reused rather than rewritten:
path::is_cmd_shell_program— already knowscmd,cmd.exe,CMD.EXEand full paths, and isalready used this way by
cmd.rs,hooks.rsandinline_args_style.file::is_unc_path— already matches bothPrefix::UNCandPrefix::VerbatimUNC. Only widenedfrom private to
pub(crate).Not keyed off the existing
cmd_verbatimflag, which would have been the shorter route: it is onlyset for inline scripts, so a file task reaching
cmd.exethroughwindows_default_file_shell_argswould slip past it.
The judgement call — happy to flip this
Error or warning? This errors. The reasoning: the neighbouring "task directory does not exist"
check only warns, but that case then fails loudly at the spawn anyway, whereas this one succeeds
in the wrong directory. Silent success in a directory the user did not choose seemed worse than a
refusal with a remedy.
The counter-argument is real, though: a task that never touches a relative path works today and
would start failing. If you would rather it warned and carried on, that is a one-line change from
bail!towarn!— say the word.Two things deliberately not done:
pushd/popd. cmd'spushdmaps a UNC to a temporary drive letterand would make this genuinely work. But mise hands the script to
cmd /cas a single commandline, so wrapping it changes quoting and exit-code propagation, and it fails when no drive letter
is free. Worth doing as its own change if you want UNC to actually work rather than be refused.
saying no.
Tests
Unit (
src/task/task_executor.rs) — the predicate pinned in both directions:cmd.exeon\\server\share\projand on the verbatim\\?\UNC\...form are refused;pwshon the samedirectory is not (the shell is half the decision);
cmd.exeonC:\projis not (the path shape isthe other half). One more checks the message names the directory,
pwsh -cand the setting.e2e-win/task_unc_dir.Tests.ps1— a task with a UNCdirunder the default shell must fail andsay so, and the same task with
shell = "pwsh -c"must not produce that message. The share does notneed to exist, because the guard fires on the shape of the path before anything spawns, which keeps
the suite free of admin rights and of a real share. The silent-relocation case above was measured by
hand rather than in CI for the same reason.
Notes
cargo fmt --allonly, plus the new Pester suite against a release binary— where, as expected, the control half passes and the guard half fails because the guard is not in
that build.
cargo testandwindows-e2eare left to CI.Summary by CodeRabbit
Bug Fixes
C:\Windows, including during cached command execution.Tests