A malicious coder can get unsound access to TCell or TLCell memory

Exploitation

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

CVSS

not scored

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

This is impossible to do by accident, but by carefully constructing marker types to be covariant, a malicious coder can cheat the singleton check in TCellOwner and TLCellOwner, giving unsound access to cell memory. This could take the form of getting two mutable references to the same memory, or a mutable reference and an immutable reference. The fix is for the crate to internally force the marker type to be invariant. This blocks the conversion between covariant types which Rust normally allows.

Published by the source

17 Jun 2022, 00:16 UTC

Last modified by the source

12 Jan 2023, 05:01 UTC

Source last checked

26 Oct 2026, 15:33 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9c9f-7x9p-4wqp

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# Patch Next advisory brief: GHSA-9c9f-7x9p-4wqp

Advisory: A malicious coder can get unsound access to TCell or TLCell memory
IDs: GHSA-9c9f-7x9p-4wqp
Record: https://patchnext.com/advisories/ghsa-9c9f-7x9p-4wqp (revision 1, source checked 26 Oct 2026, 15:33 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 fix available; fixed versions by package: qcell 0.4.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io qcell: affected < 0.4.3; fixed in 0.4.3

## Suggested inspection (read-only)
- crates.io qcell: 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 qcell.
- 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-9c9f-7x9p-4wqp (GitHub-reviewed advisory GHSA-9c9f-7x9p-4wqp lists affected ranges: crates.io qcell >=0 <0.4.3)

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