Vulnerability-Lookup

GHSA-3G72-RRQC-F76C

Vulnerability from github – Published: 2026-11-01 18:30 – Updated: 2026-11-01 18:30

Details

Prefab UI's Generative UI sandbox runs caller-supplied Python inside Pyodide, Python compiled to WebAssembly, in a Deno subprocess. The feature is documented as isolation for untrusted code, including LLM-written UI. From prefab-ui 0.14.0 through 0.20.2 the launcher starts Deno with unrestricted --allow-read, --allow-write, and --allow-net, and the runner leaves the Deno API on the JavaScript global object. Pyodide's js module proxies that global, so the Python can call Deno.readTextFileSync and Deno.writeTextFileSync. A caller who can supply the code can read and write files as the server OS user, and can persist code execution by writing a .pth file into the server virtualenv's site-packages. The usual remote path is FastMCP's GenerativeUI provider, which registers the MCP tool generate_prefab_ui and forwards that tool's code argument into this sandbox. On a FastMCP server with no authentication configured, any client who can reach the server can call the tool. With authentication, any client allowed to call tools can. Generative UI is opt-in, and the host must have Deno installed. Confirmed on prefab-ui 0.20.2. Fixed in 0.21.0: after the runtime and Prefab sources load, the runner revokes Deno read, write, and network permission before it accepts code, the process is started with --no-prompt so a permission request cannot grant them again, and bootstrap network access is limited to cdn.jsdelivr.net. The fix is commit 030f074 (pull request 538).

Severity

10.0 (Critical)


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

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-120338"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-94"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-11-01T16:18:14Z",
    "severity": "CRITICAL"
  },
  "details": "Prefab UI\u0027s Generative UI sandbox runs caller-supplied Python inside Pyodide, Python compiled to WebAssembly, in a Deno subprocess. The feature is documented as isolation for untrusted code, including LLM-written UI. From prefab-ui 0.14.0 through 0.20.2 the launcher starts Deno with unrestricted --allow-read, --allow-write, and --allow-net, and the runner leaves the Deno API on the JavaScript global object. Pyodide\u0027s js module proxies that global, so the Python can call Deno.readTextFileSync and Deno.writeTextFileSync. A caller who can supply the code can read and write files as the server OS user, and can persist code execution by writing a .pth file into the server virtualenv\u0027s site-packages. The usual remote path is FastMCP\u0027s GenerativeUI provider, which registers the MCP tool generate_prefab_ui and forwards that tool\u0027s code argument into this sandbox. On a FastMCP server with no authentication configured, any client who can reach the server can call the tool. With authentication, any client allowed to call tools can. Generative UI is opt-in, and the host must have Deno installed. Confirmed on prefab-ui 0.20.2. Fixed in 0.21.0: after the runtime and Prefab sources load, the runner revokes Deno read, write, and network permission before it accepts code, the process is started with --no-prompt so a permission request cannot grant them again, and bootstrap network access is limited to cdn.jsdelivr.net. The fix is commit 030f074 (pull request 538).",
  "id": "GHSA-3g72-rrqc-f76c",
  "modified": "2026-11-01T18:30:24Z",
  "published": "2026-11-01T18:30:23Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/PrefectHQ/prefab/security/advisories/GHSA-595q-jv4r-q7j9"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-120338"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PrefectHQ/prefab/pull/538"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PrefectHQ/prefab/commit/030f074f85e0b1be0dd44b0283185aecb26337a2"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PrefectHQ/prefab"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PrefectHQ/prefab/releases/tag/v0.14.0"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PrefectHQ/prefab/releases/tag/v0.20.2"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PrefectHQ/prefab/releases/tag/v0.21.0"
    },
    {
      "type": "WEB",
      "url": "https://pypi.org/project/prefab-ui"
    },
    {
      "type": "WEB",
      "url": "https://pypi.org/project/prefab-ui/0.21.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-120338 (GCVE-0-2026-120338)

Vulnerability from cvelistv5 – Published: 2026-11-01 15:24 – Updated: 2026-11-01 15:24

Title

Prefab UI Pyodide sandbox escape to host RCE

Summary

Severity

10 (Critical)


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

9.9 (Critical)


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

CWE

CWE-693 - Protection Mechanism Failure
CWE-94 - Improper Control of Generation of Code ('Code Injection')
CWE-269 - Improper Privilege Management

Assigner

JFROG CNA under the mitre root

CNA scorecard B 76/100 over 66 records in the last 180 days details

References

9 references

URL	Tags
https://github.com/PrefectHQ/prefab	product
https://pypi.org/project/prefab-ui/	product
https://github.com/PrefectHQ/prefab/security/advi…	vendor-advisory
https://github.com/PrefectHQ/prefab/pull/538	patch
https://github.com/PrefectHQ/prefab/commit/030f07…	patch
https://github.com/PrefectHQ/prefab/releases/tag/…	release-notes
https://pypi.org/project/prefab-ui/0.21.0/	release-notes
https://github.com/PrefectHQ/prefab/releases/tag/…	technical-description
https://github.com/PrefectHQ/prefab/releases/tag/…	technical-description

Impacted products

1 product

Vendor	Product	Version
PrefectHQ	prefab-ui	Affected: 0.14.0 , < 0.21.0 (semver)

Credits

Yuval Moravchick JFrog Security Research

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "collectionURL": "https://pypi.org/project/prefab-ui/",
          "defaultStatus": "unaffected",
          "packageName": "prefab-ui",
          "product": "prefab-ui",
          "programFiles": [
            "src/prefab_ui/sandbox/_pyodide.py",
            "src/prefab_ui/sandbox/runner.js"
          ],
          "repo": "git://github.com/PrefectHQ/prefab",
          "vendor": "PrefectHQ",
          "versions": [
            {
              "lessThan": "0.21.0",
              "status": "affected",
              "version": "0.14.0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Yuval Moravchick"
        },
        {
          "lang": "en",
          "type": "coordinator",
          "value": "JFrog Security Research"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cp\u003ePrefab UI\u0027s Generative UI sandbox runs caller-supplied Python inside Pyodide, Python compiled to WebAssembly, in a Deno subprocess. The feature is documented as isolation for untrusted code, including LLM-written UI. From prefab-ui 0.14.0 through 0.20.2 the launcher starts Deno with unrestricted --allow-read, --allow-write, and --allow-net, and the runner leaves the Deno API on the JavaScript global object. Pyodide\u0027s js module proxies that global, so the Python can call Deno.readTextFileSync and Deno.writeTextFileSync. A caller who can supply the code can read and write files as the server OS user, and can persist code execution by writing a .pth file into the server virtualenv\u0027s site-packages. The usual remote path is FastMCP\u0027s GenerativeUI provider, which registers the MCP tool generate_prefab_ui and forwards that tool\u0027s code argument into this sandbox. On a FastMCP server with no authentication configured, any client who can reach the server can call the tool. With authentication, any client allowed to call tools can. Generative UI is opt-in, and the host must have Deno installed. Confirmed on prefab-ui 0.20.2. Fixed in 0.21.0: after the runtime and Prefab sources load, the runner revokes Deno read, write, and network permission before it accepts code, the process is started with --no-prompt so a permission request cannot grant them again, and bootstrap network access is limited to cdn.jsdelivr.net. The fix is commit 030f074 (pull request 538).\u003c/p\u003e"
            }
          ],
          "value": "Prefab UI\u0027s Generative UI sandbox runs caller-supplied Python inside Pyodide, Python compiled to WebAssembly, in a Deno subprocess. The feature is documented as isolation for untrusted code, including LLM-written UI. From prefab-ui 0.14.0 through 0.20.2 the launcher starts Deno with unrestricted --allow-read, --allow-write, and --allow-net, and the runner leaves the Deno API on the JavaScript global object. Pyodide\u0027s js module proxies that global, so the Python can call Deno.readTextFileSync and Deno.writeTextFileSync. A caller who can supply the code can read and write files as the server OS user, and can persist code execution by writing a .pth file into the server virtualenv\u0027s site-packages. The usual remote path is FastMCP\u0027s GenerativeUI provider, which registers the MCP tool generate_prefab_ui and forwards that tool\u0027s code argument into this sandbox. On a FastMCP server with no authentication configured, any client who can reach the server can call the tool. With authentication, any client allowed to call tools can. Generative UI is opt-in, and the host must have Deno installed. Confirmed on prefab-ui 0.20.2. Fixed in 0.21.0: after the runtime and Prefab sources load, the runner revokes Deno read, write, and network permission before it accepts code, the process is started with --no-prompt so a permission request cannot grant them again, and bootstrap network access is limited to cdn.jsdelivr.net. The fix is commit 030f074 (pull request 538)."
        }
      ],
      "metrics": [
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            "attackComplexity": "LOW",
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            "availabilityImpact": "HIGH",
            "baseScore": 10,
            "baseSeverity": "CRITICAL",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "CHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "FastMCP server with GenerativeUI enabled, Deno installed, and no authentication configured"
            }
          ]
        },
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 9.9,
            "baseSeverity": "CRITICAL",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "LOW",
            "scope": "CHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "Authenticated client allowed to call tools on a server that executes untrusted code in the Generative UI sandbox"
            }
          ]
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          "descriptions": [
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              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-269",
              "description": "CWE-269: Improper Privilege Management",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-11-01T15:24:54.158Z",
        "orgId": "48a46f29-ae42-4e1d-90dd-c1676c1e5e6d",
        "shortName": "JFROG"
      },
      "references": [
        {
          "name": "Prefab repository",
          "tags": [
            "product"
          ],
          "url": "https://github.com/PrefectHQ/prefab"
        },
        {
          "name": "prefab-ui on PyPI",
          "tags": [
            "product"
          ],
          "url": "https://pypi.org/project/prefab-ui/"
        },
        {
          "name": "GHSA-595q-jv4r-q7j9",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://github.com/PrefectHQ/prefab/security/advisories/GHSA-595q-jv4r-q7j9"
        },
        {
          "name": "Refresh dependencies and fix renderer and sandbox regressions (fix pull request)",
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          "url": "https://github.com/PrefectHQ/prefab/commit/030f074f85e0b1be0dd44b0283185aecb26337a2"
        },
        {
          "name": "v0.21.0",
          "tags": [
            "release-notes"
          ],
          "url": "https://github.com/PrefectHQ/prefab/releases/tag/v0.21.0"
        },
        {
          "name": "prefab-ui 0.21.0",
          "tags": [
            "release-notes"
          ],
          "url": "https://pypi.org/project/prefab-ui/0.21.0/"
        },
        {
          "name": "v0.20.2 (confirmed affected)",
          "tags": [
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          "url": "https://github.com/PrefectHQ/prefab/releases/tag/v0.20.2"
        },
        {
          "name": "v0.14.0 (first release with the sandbox)",
          "tags": [
            "technical-description"
          ],
          "url": "https://github.com/PrefectHQ/prefab/releases/tag/v0.14.0"
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "timeline": [
        {
          "lang": "en",
          "time": "2026-03-24T17:21:00.000Z",
          "value": "Pyodide sandbox added with --allow-read, --allow-write, and --allow-net (commit fc4362f3, pull request 334)"
        },
        {
          "lang": "en",
          "time": "2026-03-27T02:36:00.000Z",
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          "lang": "en",
          "time": "2026-06-03T02:13:00.000Z",
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        },
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          "lang": "en",
          "time": "2026-08-05T16:12:00.000Z",
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        },
        {
          "lang": "en",
          "time": "2026-10-25T18:48:00.000Z",
          "value": "Fix merged in pull request 538 (commit 030f074). The runner revokes read, write, and network permission before accepting code."
        },
        {
          "lang": "en",
          "time": "2026-10-26T19:00:00.000Z",
          "value": "prefab-ui 0.21.0 published on PyPI with the fix. No vendor advisory text was published with the release."
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    "datePublished": "2026-11-01T15:24:54.158Z",
    "dateReserved": "2026-11-01T15:12:50.987Z",
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

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