It was reported proc-macro1 contained a build script that would download a malicious payload.

This crate had two versions, both published on 2026-08-20. The crate was removed from crates.io and related user accounts were locked.

This crate was used as part of a malware campaign targeted at users of arrayref, which was downloaded 2,285 times before being removed; see the arrayref advisory for more detail.

Thanks to the Research Team at Nextron Systems GmbH for reporting this to the Rust security response working group, and thanks to Emily Albini for coordinating with the crates.io and infra-admin teams.