CVE-2026-54338 JupyterHub: Unauthenticated Denial of Service via Unbounded Username Logging on Failed Login
Unauthenticated attackers can cause denial of service by submitting invalid login attempts with unbounded usernames, consuming logging and storage resources.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54338?
CVE-2026-54338 is a medium-severity denial of service vulnerability in jupyterhub, published on 7 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. Prior to 5.5.0, invalid input to form-based login authenticators can place an unbounded attacker-controlled username in failed-login logs, allowing an unauthenticated attacker to consume logging and storage resources. This issue is fixed in version 5.5.0.
Weakness: CWE-400
Which versions are affected by CVE-2026-54338?
4 open source packages ship an affected version, including jupyterhub.
| Package | Affected | Fixed in |
|---|---|---|
jupyterhub Bitnami | All versions | 5.5.0 |
jupyterhub PyPI | All versions | 5.5.0 |
jupyterhub PyPI | All versions | 5.5.0 |
jupyterhub PyPI | All versions | 5.5.0 |
How do I fix CVE-2026-54338?
Upgrade jupyterhub to 5.5.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-54338 being exploited?
There is no known exploitation of CVE-2026-54338 in the wild and no public exploit code.
Sources
Also known as BIT-jupyterhub-2026-54338, DEBIAN-CVE-2026-54338, GHSA-p43p-whwx-q52h, PYSEC-2026-3853, UBUNTU-CVE-2026-54338.