CVE-2026-40035: Unfurl through 2025.08 contains an improper input validation vulnerability in config parsing that enables Flas

Q: How do I fix CVE-2026-40035?

unfurl: upgrade to newer than 2025.08. Exact commands for each OS are on this page.

Q: Is CVE-2026-40035 being exploited?

CVE-2026-40035 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-40035 affect?

CVE-2026-40035 affects unfurl. Severity is critical (CVSS 9.1). 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

Q: How urgent is CVE-2026-40035?

Priority 53/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.1REMOTEUPGRADE

CVE-2026-40035 is a critical-severity flaw (CVSS 9.1) affecting unfurl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 54%)
CISA exploited list	No
Weakness	CWE-489
Published	2026-04-08
Last modified	2026-10-08

Publisher (CNA): VulnCheck · Vendor: ryandfir

Last updated 2026-10-08 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-08 22:16 UTCPublished CVE record published
2026-10-08 16:17 UTCUpdated Record last modified

ryandfir unfurl UPGRADE

Affected: <= 2025.08

Fixed in: newer than 2025.08

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy unfurl || rpm -q unfurl || unfurl --version

2. UPGRADE to newer than 2025.08 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade unfurl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade unfurl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-40035?

unfurl: upgrade to newer than 2025.08. Exact commands for each OS are on this page.

Is CVE-2026-40035 being exploited?

CVE-2026-40035 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-40035 affect?

CVE-2026-40035 affects unfurl. Severity is critical (CVSS 9.1). 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

How urgent is CVE-2026-40035?

Priority 53/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

Flask vulnerabilities

Related CVEs

CVE-2026-40036 HIGH 7.5 UPGRADE Unfurl before 2026.04 contains an unbounded zlib decompression vulnerability in parse_compressed.py that allow

References

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