diff --git a/posts/2024-09-04-cve-2024-43402.md b/posts/2024-09-04-cve-2024-43402.md new file mode 100644 index 000000000..dcd061ca6 --- /dev/null +++ b/posts/2024-09-04-cve-2024-43402.md @@ -0,0 +1,63 @@ +--- +layout: post +title: "Security advisory for the standard library (CVE-2024-43402)" +author: The Rust Security Response WG +--- + +On April 9th, 2024, the Rust Security Response WG disclosed [CVE-2024-24576][1], +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][1] 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][2] 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][1] 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][3]. + +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. + +[1]: https://blog.rust-lang.org/2024/04/09/cve-2024-24576.html +[2]: https://learn.microsoft.com/en-us/troubleshoot/windows-client/shell-experience/file-folder-name-whitespace-characters +[3]: https://www.rust-lang.org/policies/security