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CVE-2025-66627

Wasmi's Linear Memory has a Critical Use After Free Vulnerability

8.4 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Local
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

0.15%Up 0.1 points since Dec 9, 2025
90%50%10%1%

What each source reports

CVE List Score used 8.4

Wasmi's Linear Memory has a Critical Use After Free Vulnerability

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.

Record
CVE-2025-66627
CVSS 3.1
8.4 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-416
Updated
2026-11-02
EUVDEUVD-2025-201826 8.4

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.

Record
EUVD-2025-201826
CVSS 3.1
8.4 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-g4v2-cjqp-rfmq 8.4

Critical Use-After-Free in Wasmi's Linear Memory

Summary

A use-after-free vulnerability has been discovered in the linear memory implementation of Wasmi. This issue can be triggered by a WebAssembly module under certain memory growth conditions, potentially leading to memory corruption, information disclosure, or code execution.

Impact

  • Confidentiality: High – attacker-controlled memory reads possible.
  • Integrity: High – memory corruption may allow arbitrary writes.
  • Availability: High – interpreter crashes possible.

Affected Versions

Wasmi v0.41.0 through Wasmi v1.0.0.

Workarounds

  • Upgrade to the latest patched version of Wasmi.
  • Consider limiting the maximum linear memory sizes where feasible.

Credits

This vulnerability was discovered by Robert T. Morris (RTM).

Record
GHSA-g4v2-cjqp-rfmq
CVSS 3.1
8.4 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-416
Updated
2026-11-02
NVD 8.4

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.

Record
CVE-2025-66627
CVSS 3.1
8.4 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 3.1
7.8 HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-416
Updated
2026-11-02
OSV 8.4

Wasmi's Linear Memory has a Critical Use After Free Vulnerability

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.

Record
CVE-2025-66627
CVSS 3.1
8.4 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-416
Updated
2026-11-02
OSVGHSA-g4v2-cjqp-rfmq 8.4

Critical Use-After-Free in Wasmi's Linear Memory

Summary

A use-after-free vulnerability has been discovered in the linear memory implementation of Wasmi. This issue can be triggered by a WebAssembly module under certain memory growth conditions, potentially leading to memory corruption, information disclosure, or code execution.

Impact

  • Confidentiality: High – attacker-controlled memory reads possible.
  • Integrity: High – memory corruption may allow arbitrary writes.
  • Availability: High – interpreter crashes possible.

Affected Versions

Wasmi v0.41.0 through Wasmi v1.0.0.

Workarounds

  • Upgrade to the latest patched version of Wasmi.
  • Consider limiting the maximum linear memory sizes where feasible.

Credits

This vulnerability was discovered by Robert T. Morris (RTM).

Record
GHSA-g4v2-cjqp-rfmq
CVSS 3.1
8.4 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-416
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
wasmi
crates.io
 0.41.0 up to 0.41.2
0.41.2
wasmi
crates.io
 0.42.0 up to 0.47.1
0.47.1
wasmi
crates.io
 0.50.0 up to 0.51.3
0.51.3
wasmi
crates.io
 1.0.0 up to 1.0.1
1.0.1

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2025-66627 is a high vulnerability (CVSS 8.4) in Wasmi-labs Wasmi, published December 8, 2025. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.15%, the 3rd percentile. Fixed in wasmi 0.41.2.

References

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