How severe is CVE-2020-26261?

CVE-2020-26261 has a CVSS score of 7.9/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2020-26261?

CVE-2020-26261 affects the following packages: jupyterhub-systemdspawner (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2020-26261?

Update jupyterhub-systemdspawner to 0.15.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-26261 is resolved across your whole dependency graph.

How do I detect CVE-2020-26261 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jupyterhub-systemdspawner, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2020-26261 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2020-26261 actively exploited in the wild?

No public exploit code has been indexed for CVE-2020-26261 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2020-26261?

CVE-2020-26261 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 40th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2020-26261?

CVE-2020-26261 is classified as CWE-668 (CWE-668). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2020-26261 published, and has it been updated?

CVE-2020-26261 was published on December 9, 2020 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2020-26261 — jupyterhub-systemdspawner

HIGHFix: jupyterhub/systemdspawner@a4d08fd

CVE-2020-26261 is a high-severity (CVSS 7.9) CWE-668 vulnerability in jupyterhub-systemdspawner. A fix is available for jupyterhub-systemdspawner — see the affected versions and patch details below.

user-readable api tokens in systemd units for JupyterHub

Also known asGHSA-cg54-gpgr-4rm6PYSEC-2020-52

Published

Dec 9, 2020

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2020-26261 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐍jupyterhub-systemdspawner

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Impact

user API tokens issued to single-user servers are specified in the environment of systemd units, which are accessible to all users.

In particular, the-littlest-jupyterhub is affected, which uses systemdspawner by default.

Patches

Patched in jupyterhub-systemdspawner v0.15

Workarounds

No workaround other than upgrading systemdspawner to 0.15

For more information

If you have any questions or comments about this advisory:

Open a thread in the Jupyter forum
Email us at [email protected]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`jupyterhub-systemdspawner`	all versions	0.15.0`pip install --upgrade 'jupyterhub-systemdspawner==0.15.0'`

Affected Products

1 product · 1 configurations

Application

systemdspawnerjupyterhub

< 0.15

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jupyterhub-systemdspawner, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update jupyterhub-systemdspawner to 0.15.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-26261 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Impact user API tokens issued to single-user servers are specified in the environment of systemd units, which are accessible to all users. In particular, the-littlest-jupyterhub is affected, which uses systemdspawner by default. ### Patches Patched in jupyterhub-systemdspawner v0.15 ### Workarounds No workaround other than upgrading systemdspawner to 0.15 ### For more information If you have any questions or comments about this advisory: * Open a thread in [the Jupyter forum](https://discourse.jupyter.org) * Email us at [[email protected]](mailto:[email protected])