---
title: "CVE-2026-100723: vm2 before 3.12.2 Memory Disclosure via zlib Buffer Pool"
url: https://erroneo.us/security/cve/CVE-2026-100723/
description: "CVE-2026-100723 (patriksimek vm2): vm2 before 3.12.2 does not apply its Buffer backing-store ownership invariant (byteOffset === 0 and buffer.byteLength ===…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-09-27
date_modified: 2026-10-07
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-100723"
kev: false
cvss: 6.9
epss: 0.00316
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-100723: vm2 before 3.12.2 Memory Disclosure via zlib Buffer Pool

**Signal:** Normal patch cycle. No exploitation signal; fix it in your next routine update if you are affected. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.3% , percentile 23: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 23% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Editorial verdict: Check exposure. vm2: 22 Critical Sandbox Escapes, Fixed in 3.12.2 — If anything outside your trust boundary can get code into vm2, upgrade to 3.12.2 today and plan to move that code out of process; if vm2 only runs your own code, upgrade on a normal cycle.

## What it is

vm2 before 3.12.2 does not apply its Buffer backing-store ownership invariant (byteOffset === 0 and buffer.byteLength === length) to Buffers returned from host builtin modules. When an application explicitly exposes Node's zlib module through NodeVM's builtin allowlist (require: { builtin: ['zlib'] }), zlib.deflateSync can return a Buffer backed by Node's shared small-buffer pool whose .buffer is the entire pool. Untrusted guest code can construct a full-width view of that ArrayBuffer (Buffer.from(result.buffer, 0, result.buffer.byteLength)) to read and modify bytes belonging to unrelated host buffers, disclosing and corrupting host-realm memory across the sandbox boundary.

## Affected products (CVE record)

- patriksimek vm2: < 3.12.2

## Severity

- VulnCheck CVSS 4.0: 6.9 `CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N`
- VulnCheck CVSS 3.1: 7.5 `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable no , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.32% probability of exploitation activity in the next 30 days; percentile 23.

## Sources

- [GitHub Security Advisory (GHSA-489w-w794-jq94)](https://github.com/patriksimek/vm2/security/advisories/GHSA-489w-w794-jq94)
- [Patch Commit](https://github.com/patriksimek/vm2/commit/4f2508abeb252aa86eb6761c78b3b000248fb089)
- [Patch Commit](https://github.com/patriksimek/vm2/commit/5214b02ef13b82497fcb917b45320dfd014ffd09)
- [CVE.org record CVE-2026-100723](https://www.cve.org/CVERecord?id=CVE-2026-100723)
- [NVD entry CVE-2026-100723](https://nvd.nist.gov/vuln/detail/CVE-2026-100723)
- [VulnCheck Advisory: vm2 before 3.12.2 Memory Disclosure via zlib Buffer Pool](https://www.vulncheck.com/advisories/vm2-before-3.12.2-memory-disclosure-via-zlib-buffer-pool)

---
Source page: https://erroneo.us/security/cve/CVE-2026-100723/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt