Upgrading to Rust 1.94.1: A Guide to Recent Regressions and Security Patches

Overview

Rust 1.94.1 is a point release that addresses three regressions introduced in version 1.94.0 and a security vulnerability in Cargo's tar handling. While point releases are typically minor, this update is important for developers using certain platforms or tools. This guide walks you through the update process, explains each fix in detail, and helps you avoid common pitfalls.

Prerequisites

• Existing Rust installation via rustup — If you haven't yet installed Rust, follow the instructions at rustup.rs first.
• Basic familiarity with the Rust toolchain — You should know how to run commands in your terminal and understand the concept of Rust editions and channels.
• Access to a terminal or command prompt — All steps here are command-line based.

Step-by-Step Instructions

1. Check Your Current Rust Version

Before updating, it's good practice to confirm which version you're currently running:

rustc --version

This will output something like rustc 1.94.0 (4d826b1d0 2025-03-15). If you're already on 1.94.1, you're all set.

2. Update to Rust 1.94.1

Run the following command to upgrade your stable toolchain to the latest point release:

rustup update stable

This fetches the new compiler, tools, and libraries. After completion, verify the update:

rustc --version
# Should now show: rustc 1.94.1 (a1b2c3d4e 2025-03-22)

3. Understand the Regression Fixes

Rust 1.94.1 resolves three regressions from the 1.94.0 release. Let's examine each:

Fix for std::thread::spawn on wasm32-wasip1-threads

In 1.94.0, calling std::thread::spawn on WebAssembly targets using the wasm32-wasip1-threads variant could lead to a panic or undefined behavior. This was a regression that broke multithreaded WebAssembly modules built with Rust.

Example code that would have failed:

use std::thread;
fn main() {
    let handle = thread::spawn(|| {
        println!("Hello from a WebAssembly thread");
    });
    handle.join().unwrap();
}

After 1.94.1, the above code works correctly. If you're targeting Wasm with threading support, update immediately.

Removal of New Methods from std::os::windows::fs::OpenOptionsExt

Version 1.94.0 added several unstable methods to the OpenOptionsExt trait on Windows. However, because the trait is not sealed, adding non-default methods broke external implementations — users implementing the trait would suddenly have to implement those new methods. To avoid breaking changes, the team removed the additions. No code changes are needed for most developers, but if you relied on those unstable methods, they are no longer available. Consult the tracking issue for alternatives.

Clippy ICE in match_same_arms

An internal compiler error (ICE) was triggered in Clippy when using the match_same_arms lint on certain patterns. For example:

fn main() {
    let x = 42;
    match x {
        1 => println!("one"),
        2 => println!("two"),
        1 => println!("duplicate arm"), // duplicate arm; would cause ICE
        _ => println!("other"),
    }
}

In 1.94.0, this would crash Clippy. Now it correctly reports the duplicate arm and continues analysis.

4. Cargo Fixes

Cargo also received two important updates in 1.94.1:

Downgrade curl-sys to 0.4.83

Some users on FreeBSD experienced certificate validation errors when using crates that depend on curl-sys. The issue was traced to a version bump in 1.94.0. The fix downgrades curl-sys back to 0.4.83, restoring proper certificate handling.

Update tar to 0.4.45 (Security Fix)

Two CVEs (CVE-2026-33055 and CVE-2026-33056) were discovered in the tar crate used by Cargo. The vulnerabilities could allow a malicious crate to perform path traversal or symlink attacks during extraction. Cargo now uses tar 0.4.45, which patches these issues. Users of crates.io are not affected directly, but running cargo publish or cargo package on untrusted archives could be risky.

Common Mistakes

• Not updating after installation — If you installed Rust with rustup but never ran rustup update stable, you may be on an outdated version. Always keep your toolchain current.
• Using the wrong channel — This guide covers stable Rust. If you use nightly or beta, the version numbers differ. To switch back to stable: rustup default stable.
• Ignoring security updates — The tar CVE affects anyone who publishes or extracts crates locally. Even if you don't think you're impacted, updating is a best practice.
• Forgetting to restart — After updating, close and reopen your terminal or IDE to ensure the new toolchain is picked up.
• Assuming all regressions are fixed — While 1.94.1 fixes three regressions, other issues may exist. Always test your project thoroughly after an update.

Summary

Rust 1.94.1 is a maintenance release that corrects three regressions (WebAssembly thread spawning, Windows file trait extendibility, and Clippy crash) and patches a security vulnerability in Cargo's tar handling. Updating is as simple as rustup update stable. If you develop for Wasm with threads, use Windows, or rely on Clippy, this update is especially important. For everyone else, it's a routine but recommended upgrade to keep your toolchain stable and secure.