# RUSTSEC-2026-0265: `proc-macro1` was removed from crates.io due to malicious code

> A malicious Rust crate named proc-macro1 was published to crates.io, allowing attackers to execute arbitrary code via its build script.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 20 Aug 2026

## What is RUSTSEC-2026-0265?

RUSTSEC-2026-0265 is a vulnerability in proc-macro1, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

## Which versions are affected by RUSTSEC-2026-0265?

1 open source package ship an affected version, including proc-macro1.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `proc-macro1` | crates.io | From 0.0.0-0 | None |

## How do I fix RUSTSEC-2026-0265?

No fix has been published for RUSTSEC-2026-0265 yet. Limit exposure of the affected software until one is available.

## Is RUSTSEC-2026-0265 being exploited?

There is no known exploitation of RUSTSEC-2026-0265 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0265 and fix it if it is affected.

What it is: RUSTSEC-2026-0265 is a vulnerability in proc-macro1, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of RUSTSEC-2026-0265 in the wild and no public exploit code.

Affected packages and fixed versions:
- proc-macro1 (crates.io): affected from 0.0.0-0; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/RUSTSEC-2026-0265/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0265/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0265

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0265/
Summaries are generated and may contain mistakes; the official description above is the record.