Summary
| Parameter | Value |
|---|---|
| CVE ID | CVE-2026-40035 |
| Alert Source | GitHub Advisory - Critical Vulnerability |
| CVE Publication Year | 2026 |
| Date Published | 2026-04-09 |
| Vendor | Flask |
| Product | Flask |
| CVSS Score | 9.1 (critical) |
| EPSS Score | No data |
| CISA KEV | No |
| Ransomware | Not confirmed |
Vulnerability Description
Unfurl through 2025.08 contains an improper input validation vulnerability in config parsing that enables Flask debug mode by default. The debug configuration value is read as a string and passed directly to app.run(), causing any non-empty string to evaluate truthy, allowing attackers to access the Werkzeug debugger and disclose sensitive information or achieve remote code execution.
Required Actions
Apply vendor patches or mitigations as soon as available.
Who Is Affected?
This vulnerability affects Flask by Flask. Check if your organization uses this software and requires updates.
Sources
Need help securing your systems? nFlo team offers vulnerability management and 24/7 SOC services. Contact us.
How can nFlo help?
If your organization uses products affected by this vulnerability, contact us. We can help with:
- Verifying whether your systems are at risk
- Implementing patches and risk mitigation
- Monitoring for exploitation attempts in your environment
Useful resources:
