Incorrect reliance on Trait memory layout in mopa

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-2021-45695: 1.70% estimated exploitation activity in the next 30 days; percentile 77.25 (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.

The mopa crate redefines the deprecated TraitObject struct from core::raw. This is done to then transmute a reference to a trait object (&dyn Trait for any trait Trait) into this struct and retrieve the data field for the purpose of downcasting. This is used to implement downcastrefunchecked(), in terms of which downcastref() is also implemented. Same goes for mutable reference downcasting and Box downcasting. The Rust compiler explicitly reserves the right to change the memory layout of &dyn Trait for any trait Trait. The worst case scenario is that it swaps data and vtable, making an executable location breach and compromisation of ASLR possible, since reads from data would read vtable instead. Likewise, arbitrary code execution is also theoretically possible if reads of vtable generated by the compiler read data instead.

Published by the source

6 Jan 2022, 22:11 UTC

Last modified by the source

13 Jun 2023, 18:34 UTC

Source last checked

26 Oct 2026, 15:34 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-2gxj-qrp2-53jv

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

# Patch Next advisory brief: CVE-2021-45695

Advisory: Incorrect reliance on Trait memory layout in mopa
IDs: CVE-2021-45695, GHSA-2gxj-qrp2-53jv
Record: https://patchnext.com/advisories/cve-2021-45695 (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 response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io mopa: affected <= 0.2.2

## Suggested inspection (read-only)
- crates.io mopa: 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 mopa.
- 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-2gxj-qrp2-53jv (GitHub-reviewed advisory GHSA-2gxj-qrp2-53jv lists affected ranges: crates.io mopa >=0 <=0.2.2)

Commands are suggestions: review each one before running it.