Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

9.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-40035: 0.56% estimated exploitation activity in the next 30 days; percentile 46.46 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default. Details - unfurl/app.py:webapp() reads debug via config['UNFURLAPP'].get('debug'), which returns a string. - UnfurlApp.init passes that string directly to app.run(debug=unfurldebug, ...). - If unfurl.ini omits debug, the default argument is the string "True". - As a result, debug mode is effectively always on and cannot be reliably disabled via config. PoC 1. Create a local unfurl.ini with debug = False under [UNFURLAPP]. 2. Run the server using unfurlapp (or python -c 'from unfurl.app import webapp; webapp()'). 3. Observe server logs showing Debug mode: on / Debugger is active!. 4. The included PoC script securitypoc/pocdebugmode.py --spawn automates this check. PoC Script (inline) Impact If the service is exposed…

Published by the source

29 Jan 2026, 15:32 UTC

Last modified by the source

8 Jul 2026, 08:26 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vg9h-jx4v-cwx2

2. Revision 3 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-vg9h-jx4v-cwx2

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-vg9h-jx4v-cwx2

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# Patch Next advisory brief: CVE-2026-40035

Advisory: Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)
IDs: CVE-2026-40035, GHSA-vg9h-jx4v-cwx2
Record: https://patchnext.com/advisories/ghsa-vg9h-jx4v-cwx2 (revision 4, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI dfir-unfurl: affected <= 20250810

## Suggested inspection (read-only)
- `python -m pip show dfir-unfurl`: prints the installed version. Run with the environment that serves production active.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on dfir-unfurl.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-vg9h-jx4v-cwx2 (GitHub-reviewed advisory GHSA-vg9h-jx4v-cwx2 lists affected ranges: PyPI dfir-unfurl >=0 <=20250810)
- Verified: https://osv.dev/vulnerability/GHSA-vg9h-jx4v-cwx2 (OSV record GHSA-vg9h-jx4v-cwx2 lists affected ranges: PyPI dfir-unfurl >=0 <=20250810)

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