Remote code execution via string-parsed debug setting
Published Apr 8, 2026 · Updated Apr 8, 2026
Improper input validation in Unfurl through 2025.08 allows remote attackers to expose the Werkzeug debugger through the web app. The web_app function reads the debug setting as a string, and UnfurlApp.init passes it directly to app.run(), so even "False" is truthy. When the service is exposed beyond localhost, remote attackers can read stack traces and environment details and execute code if they obtain the debugger PIN.
Summary
What happened
Improper input validation in Unfurl through 2025.08 allows remote attackers to expose the Werkzeug debugger through the web app. The web_app function reads the debug setting as a string, and UnfurlApp.init passes it directly to app.run(), so even "False" is truthy. When the service is exposed beyond localhost, remote attackers can read stack traces and environment details and execute code if they obtain the debugger PIN.
The record
- CVE
- CVE-2026-40035
- Published
- Apr 8, 2026
- Updated
- Apr 8, 2026
- Vendor
- Obsidian Forensics
- Product
- Unfurl
- Classifications
- CWE-489, CAPEC-661, CAPEC-121, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 8, 2026CVE publishedPublication date reported by the CVE source.
- Apr 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <=2025.08
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Inline Werkzeug debugger exposure PoCproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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