Use after free in nano_arena

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2021-28032: 1.53% estimated exploitation activity in the next 30 days; percentile 74.74 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Affected versions of this crate assumed that Borrow<Idx was guaranteed to return the same value on .borrow(). The borrowed index value was used to retrieve a mutable reference to a value. If the Borrow<Idx implementation returned a different index, the split arena would allow retrieving the index as a mutable reference creating two mutable references to the same element. This violates Rust's aliasing rules and allows for memory safety issues such as writing out of bounds and use-after-frees. The flaw was corrected in commit 6b83f9d by storing the .borrow() value in a temporary variable.

Published by the source

25 Aug 2021, 20:52 UTC

Last modified by the source

13 Jun 2023, 20:02 UTC

Source last checked

26 Oct 2026, 15:34 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-wp34-mqw5-jj85

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# Patch Next advisory brief: CVE-2021-28032

Advisory: Use after free in nano_arena
IDs: CVE-2021-28032, GHSA-wp34-mqw5-jj85
Record: https://patchnext.com/advisories/cve-2021-28032 (revision 1, source checked 26 Oct 2026, 15:34 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nano_arena 0.5.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io nano_arena: affected < 0.5.2; fixed in 0.5.2

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

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nano_arena.
- 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://github.com/advisories/GHSA-wp34-mqw5-jj85 (GitHub-reviewed advisory GHSA-wp34-mqw5-jj85 lists affected ranges: crates.io nano_arena >=0 <0.5.2)

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