On April 9th, 2024, the Rust Security Response WG disclosed CVE-2024-24576, where std::process::Command incorrectly escaped arguments when invoking batch files on Windows. We were notified that our fix for the vulnerability was incomplete, and it was possible to bypass the fix when the batch file name had trailing whitespace or periods (which are ignored and stripped by Windows).

The severity of the incomplete fix is low, due to the niche conditions needed to trigger it. Note that calculating the CVSS score might assign a higher severity to this, but that doesn't take into account what is required to trigger the incomplete fix.

The incomplete fix is identified by CVE-2024-43402.

Overview

Refer to the advisory for CVE-2024-24576 for details on the original vulnerability.

To determine whether to apply the cmd.exe escaping rules, the original fix for the vulnerability checked whether the command name ended with .bat or .cmd. At the time that seemed enough, as we refuse to invoke batch scripts with no file extension.

Unfortunately, Windows removes trailing whitespace and periods when parsing file paths. For example, .bat. . is interpreted by Windows as .bat, but our original fix didn't check for that.

Mitigations

If you are affected by this, and you are using Rust 1.77.2 or greater, you can remove the trailing whitespace (ASCII 0x20) and trailing periods (ASCII 0x2E) from the batch file name to bypass the incomplete fix and enable the mitigations.

Rust 1.81.0, due to be released on September 5th 2024, will update the standard library to apply the CVE-2024-24576 mitigations to all batch files invocations, regardless of the trailing chars in the file name.

Affected versions

All Rust versions before 1.81.0 are affected, if your code or one of your dependencies invoke a batch script on Windows with trailing whitespace or trailing periods in the name, and pass untrusted arguments to it.

Acknowledgements

We want to thank Kainan Zhang (@4xpl0r3r) for responsibly disclosing this to us according to the Rust security policy.

We also want to thank the members of the Rust project who helped us disclose the incomplete fix: Chris Denton for developing the fix, Amanieu D'Antras for reviewing the fix; Pietro Albini for writing this advisory; Pietro Albini, Manish Goregaokar and Josh Stone for coordinating this disclosure.