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proc-macro1 was removed from crates.io due to malicious code

What to do

Vendor response not established. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • crates.io proc-macro1

    Affected
    >= 0.0.0-0
    Fixed in
    no fixed version recorded

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
not scored
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

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][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. [arrayref-advisory]: https://rustsec.org/advisories/RUSTSEC-2026-0260.html

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from osv record RUSTSEC-2026-0265

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: rustsec-2026-0265

Advisory: `proc-macro1` was removed from crates.io due to malicious code
IDs: rustsec-2026-0265
Record: https://patchnext.com/advisories/rustsec-2026-0265 (revision 1, source checked 23 Oct 2026, 22:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io proc-macro1: affected >= 0.0.0-0

## Suggested inspection (read-only)
- crates.io proc-macro1: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on proc-macro1.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/RUSTSEC-2026-0265 (OSV record RUSTSEC-2026-0265 lists affected ranges: crates.io proc-macro1 >=0.0.0-0)

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