GHSA-g85v-wf27-67xc

Harden-Runner has a command injection weaknesses in `setup.ts` and `arc-runner.ts`

### Summary Versions of step-security/harden-runner prior to v2.10.2 contain multiple command injection weaknesses via environment variables that could potentially be exploited under specific conditions. However, due to the current execution order of pre-steps in GitHub Actions and the placement of harden-runner as the first step in a job, the likelihood of exploitation is low as the Harden-Runner action reads the environment variable during the pre-step stage. There are no known exploits at this time. ### Details 1. setup.ts:169 [1] performs `execSync` with a command that gets invoked after interpretation by the shell. This command includes an interpolated `process.env.USER` variable, which an attacker could modify (without actually creating a new user) to inject arbitrary shell expressions into this `execSync`. This may or may not be likely in practice, but I believe the hygienic way to perform the underlying operation is to use `execFileSync` or similar and bypass the underlying shell evaluation. 2. setup.ts:229 [2] has a nearly identical `execSync` to (1) above, but with `$USER` for shell-level interpolation rather than string interpolation. However, this is still injectable and would be best replaced by an `execFileSync`, per above. 3. arc-runner:40-44 [3] has an `execSync` with multiple string interpolations. Most of these do not appear immediately injectible (since they appear to come from presumed trusted API responses), but the expansion of `getRunnerTempDir()` may be injectable due to its dependence on potentially attacker-controllable environment variables (e.g. `RUNNER_TEMP`). The underlying operation appears to be a trivial file copy, so this entire subprocess should in theory be replaceable with ordinary NodeJS `fs` API calls instead. 4. arc-runner:53 [4] demonstrates the same weakness, and has the same resolution as (3). 5. arc-runner:57 demonstrates the same weakness as (3) and (4), and has the same resolution. 6. arc-runner:61 demonstrates the same weakness as (3), (4), and (5), and has the same resolution. [1]: https://github.com/step-security/harden-runner/blob/951b48540b429070694bc8abd82fd6901eb123ca/src/setup.ts#L169 [2]: https://github.com/step-security/harden-runner/blob/951b48540b429070694bc8abd82fd6901eb123ca/src/setup.ts#L229 [3]: https://github.com/step-security/harden-runner/blob/951b48540b429070694bc8abd82fd6901eb123ca/src/arc-runner.ts#L40-L44 [4]: https://github.com/step-security/harden-runner/blob/951b48540b429070694bc8abd82fd6901eb123ca/src/arc-runner.ts#L53 [5]: https://github.com/step-security/harden-runner/blob/951b48540b429070694bc8abd82fd6901eb123ca/src/arc-runner.ts#L57 [6]: https://github.com/step-security/harden-runner/blob/951b48540b429070694bc8abd82fd6901eb123ca/src/arc-runner.ts#L61