How severe is CVE-2025-66627?

CVE-2025-66627 has a CVSS score of 8.4/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2025-66627?

CVE-2025-66627 affects the following packages: wasmi (crates.io), wasmi (crates.io), wasmi (crates.io), wasmi (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2025-66627?

Update wasmi to 0.41.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66627 is resolved across your whole dependency graph.

How do I detect CVE-2025-66627 in my crates.io dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for wasmi, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2025-66627 if there is no patch (or I can't update yet)?

Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Is CVE-2025-66627 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-66627 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-66627?

CVE-2025-66627 has an EPSS (Exploit Prediction Scoring System) score of 0.1%, placing it in the 4th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2025-66627?

CVE-2025-66627 is classified as Use After Free (CWE-416). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-66627 published, and has it been updated?

CVE-2025-66627 was published on December 9, 2025 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🦀

🦀 crates.io

Not in CISA KEV

HIGH severity

CVE-2025-66627 — wasmi

HIGHFix: wasmi-labs/wasmi@0e6f0d2

CVE-2025-66627 is a high-severity (CVSS 8.4) Use After Free vulnerability in wasmi. A fix is available for wasmi — see the affected versions and patch details below.

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

Also known asGHSA-g4v2-cjqp-rfmq

Published

Dec 9, 2025

Updated

Oct 28, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Nov 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-66627.

EPSS Exploitation Probability

via FIRST.org ↗

0.1%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs4th percentile — riskier than 4% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

4 pkgs affected

🦀wasmi🦀wasmi🦀wasmi🦀wasmi

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

Description

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).

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`wasmi`	≥ 0.41.0&&< 0.41.2	0.41.2`cargo update -p wasmi --precise 0.41.2`
🦀crates.io	`wasmi`	≥ 0.42.0&&< 0.47.1	0.47.1`cargo update -p wasmi --precise 0.47.1`
🦀crates.io	`wasmi`	≥ 0.50.0&&< 0.51.3	0.51.3`cargo update -p wasmi --precise 0.51.3`
🦀crates.io	`wasmi`	≥ 1.0.0&&< 1.0.1	1.0.1`cargo update -p wasmi --precise 1.0.1`

Affected Products

1 product · 4 configurations

Application

wasmiwasmi-labs

≥ 0.51.0 && < 0.51.3

1 version

1.0.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for wasmi, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update wasmi to 0.41.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66627 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Frequently Asked Questions

### 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 l