---
title: "CVE-2026-120338: Prefab UI - Unrestricted File Read & Write and Remote Code Execution"
description: "Prefab UI 0.14.0 through 0.20.2 contains a file system read and write vulnerability caused by unrestricted Deno permissions and exposed Deno API in the JavaScript global object, letting attackers with code execution read/write files as the server OS user and persist code execution, exploit requires ability to supply code to the sandbox."
url: https://panop.io/threat-heartbeat/CVE-2026-120338/
---

# CVE-2026-120338 Prefab UI - Unrestricted File Read & Write and Remote Code Execution

Prefab UI 0.14.0 through 0.20.2 contains a file system read and write vulnerability caused by unrestricted Deno permissions and exposed Deno API in the JavaScript global object, letting attackers with code execution read/write files as the server OS user and persist code execution, exploit requires ability to supply code to the sandbox.

CVSS base score 10.0 /10

Critical

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.77% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-120338)

## Details

Type

Unrestricted File Read

Impact

File System Read, File System Write, Remote Code Execution

CVSS vector

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

Published

1 November 2026

Updated

3 November 2026

Weakness

[CWE-94](https://cwe.mitre.org/data/definitions/94.html)

## Vendor fix

Upgrade to version 0.21.0 or later where Deno permissions are revoked before code execution and network access is limited.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-120338](https://nvd.nist.gov/vuln/detail/CVE-2026-120338)
- [https://pypi.org/project/prefab-ui/0.21.0/](https://pypi.org/project/prefab-ui/0.21.0/)
- [https://github.com/PrefectHQ/prefab/releases/tag/v0.20.2](https://github.com/PrefectHQ/prefab/releases/tag/v0.20.2)
- [https://github.com/PrefectHQ/prefab/releases/tag/v0.21.0](https://github.com/PrefectHQ/prefab/releases/tag/v0.21.0)
- [https://pypi.org/project/prefab-ui/](https://pypi.org/project/prefab-ui/)
- [https://github.com/PrefectHQ/prefab](https://github.com/PrefectHQ/prefab)
- [https://github.com/PrefectHQ/prefab/commit/030f074f85e0b1be0dd44b0283185aecb26337a2](https://github.com/PrefectHQ/prefab/commit/030f074f85e0b1be0dd44b0283185aecb26337a2)
- [https://github.com/PrefectHQ/prefab/pull/538](https://github.com/PrefectHQ/prefab/pull/538)
- [https://github.com/PrefectHQ/prefab/releases/tag/v0.14.0](https://github.com/PrefectHQ/prefab/releases/tag/v0.14.0)
- [https://github.com/PrefectHQ/prefab/security/advisories/GHSA-595q-jv4r-q7j9](https://github.com/PrefectHQ/prefab/security/advisories/GHSA-595q-jv4r-q7j9)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

Panop answers these inside your environment, for this CVE and every other finding.

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