medium CVSS 6.1 EPSS <0.1%

CVE-2026-23528·Python vulnerability

Dask distributed is a distributed task scheduler for Dask. Prior to 2026.1.0, when Jupyter Lab, jupyter-server-proxy, and Dask distributed are all run together, it is possible to craft a URL which will result in code being executed by Jupyter due to a cross-side-scripting (XSS) bug in the Dask dashboard. It is possible for attackers to craft a phishing URL that assumes Jupyter Lab and Dask may be running on localhost and using default ports. If a user clicks on the malicious link it will open an error page in the Dask Dashboard via the Jupyter Lab proxy which will cause code to be executed by the default Jupyter Python kernel. This vulnerability is fixed in 2026.1.0.

Severity
medium
Software
Python
Fixed in
2026.1.0
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 1% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

Until: 2026.1.0

Fixed in: 2026.1.0

How to fix this CVE

Update Dask distributed to version 2026.1.0 or later to eliminate the XSS vulnerability in the dashboard component. This update patches the input sanitization issue that could allow arbitrary code execution when Jupyter Lab and Dask are running together. Users should prioritize this update if they expose Dask's dashboard through Jupyter Lab proxies, especially on shared or internet-facing systems.

sudo dnf update python3-dask-distributed

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

GET|POST request to /status or /health endpoints of Dask dashboard with URL-encoded payloads containing <script>, javascript:, or onerror= patterns in query parameters; commonly delivered via phishing links to localhost:8787 or similar default Dask ports

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement WAF rules to block requests to Dask dashboard endpoints (/status, /health, /api/*) containing HTML/JavaScript tags or event handler attributes in query strings and request bodies. Additionally, restrict access to Dask dashboard to internal networks only or enforce authentication at the reverse proxy level.

How to check if you are affected

  1. Run 'pip show dask-distributed' or 'pip3 show dask-distributed' to identify the installed Dask distributed version
  2. Check if Dask dashboard is exposed through Jupyter Lab by verifying reverse proxy configurations in jupyter_server_config.py or reviewing active proxy routes
  3. Search application logs for suspicious URL patterns targeting Dask dashboard endpoints, particularly those containing encoded characters or script tags in query parameters
  4. After updating, re-run 'pip show dask-distributed' and confirm the version is 2026.1.0 or higher

FAQ

What is CVE-2026-23528?

This is an XSS vulnerability in Dask distributed's dashboard that occurs when running alongside Jupyter Lab and jupyter-server-proxy. An attacker can craft a malicious URL that, when clicked by a user, executes arbitrary Python code in the Jupyter kernel context.

Is CVE-2026-23528 being actively exploited?

No, there is no evidence of active exploitation in the wild, and no public exploits are available. However, the attack requires minimal sophistication and relies on social engineering (phishing links), so it should still be remediated promptly.

What versions of Dask distributed are affected by CVE-2026-23528?

All versions of Dask distributed prior to 2026.1.0 are affected. The exact lower bound is unknown, but it is recommended to update any version below 2026.1.0.

How do I check if my server is vulnerable to CVE-2026-23528?

Run 'pip show dask-distributed' and check the version number. If it is below 2026.1.0, your installation is vulnerable. Additionally, verify that jupyter-server-proxy is configured and Jupyter Lab is accessible on the system.

Does Defensia detect CVE-2026-23528?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dask distributed is installed on a monitored server, CVE-2026-23528 will appear in your dashboard with remediation steps.

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References

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