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Malicious code in proc_macro1 (crates.io)

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
    every version
    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.

proc-macro1 is a typosquat of proc-macro2 published to crates.io by the account 'dtolney', impersonating David Tolnay (dtolnay). Its metadata forges authors 'David Tolnay ' and points repository at a nonexistent github.com/dtolnay/proc-macro1. The library source is a copy of proc-macro2 so dependent builds succeed, but build.rs reconstructs a base64-encoded URL and downloads an architecture-specific remote binary from https://23.254.165.112:9089/ over TLS with certificate validation disabled (a custom verifier that accepts any certificate), then executes it detached, passing 23.254.165.112:443 as argv[1] (command and control). On Unix it writes and runs /tmp/rust-setup; on Windows it writes %TEMP%\rust-setup.ps1 and launches it via a %TEMP%\rust-setup-launch.vbs launcher under wscript.exe. The download and execution run unconditionally on every build on a supported platform. This crate was the payload carrier pulled in by the trojanized arrayref 0.3.10 release. All versions have been…

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

    Published from osv record MAL-2026-14338

Agent brief

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

# Patch Next advisory brief: mal-2026-14338

Advisory: Malicious code in proc_macro1 (crates.io)
IDs: mal-2026-14338
Record: https://patchnext.com/advisories/mal-2026-14338 (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 every version

## 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/MAL-2026-14338 (OSV record MAL-2026-14338 lists affected ranges: crates.io proc-macro1 >=0)

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