CVE-2026-120338: Prefab UI's Generative UI sandbox runs caller-supplied Python inside Pyodide, Python compiled to
Affects prefab-uiSource GCVE Database
Not known to be exploited · CVSS 10.0 Critical · fixed in 0.21.0 : patch prefab-ui as a priority.
Data as of 1 Nov 2026, 19:01 UTC
Thin evidence
One scorer or none| CNA (JFROG) | CVSS 3.1 | 10.0 |
|---|---|---|
| CNA (JFROG) | CVSS 3.1 | 9.9 |
- Patch
- Available – fixed in 0.21.0
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 1 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 1 Nov 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
PyPIprefab-uipkg:pypi/prefab-uiOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Upgrade Prefab UI to version 0.21.0 or later, where the vulnerability is fixed by revoking Deno permissions before executing caller-supplied code, disabling permission prompts, and restricting network access. If upgrading is not immediately possible, disable the Generative UI feature or restrict access to trusted users only. The fix is implemented in commit 030f074 (pull request 538).
Description
Prefab UI's Generative UI sandbox allowed execution of caller-supplied Python code with excessive permissions in Deno subprocesses, enabling arbitrary file read/write and persistent code execution on the server. This affected versions from 0.14.0 through 0.20.2. The vulnerability was fixed in version 0.21.0 by revoking Deno permissions before code execution and restricting network access.
References
- github.com/PrefectHQ/prefab/security/advisories/GHSA-595q-jv4r-q7j9 (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2026-120338 (opens in a new tab)
- github.com/PrefectHQ/prefab/pull/538 (opens in a new tab)
- github.com/PrefectHQ/prefab/commit/030f074f85e0b1be0dd44b0283185aecb26337a2 (opens in a new tab)
- github.com/PrefectHQ/prefab (opens in a new tab)
- github.com/PrefectHQ/prefab/releases/tag/v0.14.0 (opens in a new tab)
- github.com/PrefectHQ/prefab/releases/tag/v0.20.2 (opens in a new tab)
- github.com/PrefectHQ/prefab/releases/tag/v0.21.0 (opens in a new tab)
- pypi.org/project/prefab-ui (opens in a new tab)
- pypi.org/project/prefab-ui/0.21.0 (opens in a new tab)