1# safeexec
2
3A Go module that provides a safer alternative to `exec.LookPath()` on Windows.
4
5The following, relatively common approach to running external commands has a subtle vulnerability on Windows:
6```go
7import "os/exec"
8
9func gitStatus() error {
10 // On Windows, this will result in `.\git.exe` or `.\git.bat` being executed
11 // if either were found in the current working directory.
12 cmd := exec.Command("git", "status")
13 return cmd.Run()
14}
15```
16
17Searching the current directory (surprising behavior) before searching folders listed in the PATH environment variable (expected behavior) seems to be intended in Go and unlikely to be changed: https://github.com/golang/go/issues/38736
18
19Since Go does not provide a version of [`exec.LookPath()`](https://golang.org/pkg/os/exec/#LookPath) that only searches PATH and does not search the current working directory, this module provides a `LookPath` function that works consistently across platforms.
20
21Example use:
22```go
23import (
24 "os/exec"
25 "github.com/cli/safeexec"
26)
27
28func gitStatus() error {
29 gitBin, err := safeexec.LookPath("git")
30 if err != nil {
31 return err
32 }
33 cmd := exec.Command(gitBin, "status")
34 return cmd.Run()
35}
36```
37
38## TODO
39
40Ideally, this module would also provide `exec.Command()` and `exec.CommandContext()` equivalents that delegate to the patched version of `LookPath`. However, this doesn't seem possible since `LookPath` may return an error, while `exec.Command/CommandContext()` themselves do not return an error. In the standard library, the resulting `exec.Cmd` struct stores the LookPath error in a private field, but that functionality isn't available to us.
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