CVE-2026-39844: NiceGUI is a Python-based UI framework

Q: How do I fix CVE-2026-39844?

nicegui: upgrade to 3.10.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-39844 being exploited?

CVE-2026-39844 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-2026-39844 affect?

CVE-2026-39844 affects nicegui. Severity is medium (CVSS 5.9). NiceGUI is a Python-based UI framework. Prior to 3.10.0, Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (\) in the upload filename. Applic

Q: How urgent is CVE-2026-39844?

Priority 33/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-39844 is a medium-severity flaw (CVSS 5.9) affecting nicegui. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

NiceGUI is a Python-based UI framework. Prior to 3.10.0, Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (\) in the upload filename. Applications that construct file paths using file.name (a pattern demonstrated in NiceGUI's bundled examples) are vulnerable to arbitrary file write on Windows. This vulnerability is fixed in 3.10.0.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 69%)
CISA exploited list	No
Weakness	CWE-22
Published	2026-04-08
Last modified	2026-07-24

Publisher (CNA): GitHub, Inc. · Vendor: zauberzeug

Last updated 2026-07-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-08 21:16 UTCPublished CVE record published
2026-07-24 21:10 UTCUpdated Record last modified

zauberzeug nicegui UPGRADE

Affected: < 3.10.0

Fixed in: 3.10.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 3.10.0 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nicegui

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-2026-39844?

nicegui: upgrade to 3.10.0. Exact commands for each OS are on this page.

Is CVE-2026-39844 being exploited?

CVE-2026-39844 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-2026-39844 affect?

CVE-2026-39844 affects nicegui. Severity is medium (CVSS 5.9). NiceGUI is a Python-based UI framework. Prior to 3.10.0, Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (\) in the upload filename. Applic

How urgent is CVE-2026-39844?

Priority 33/100. Remotely exploitable, no login, no user action

Software pages

Python vulnerabilities · Windows vulnerabilities

References

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