critical CVSS 9.8

CVE-2026-42796·Python vulnerability

Arelle before 2.39.10 contains an unauthenticated remote code execution vulnerability in the /rest/configure REST endpoint that accepts a plugins query parameter and forwards it to the plugin manager without authentication or authorization. Attackers can supply a URL to a malicious Python file through the plugins parameter, causing the Arelle webserver to download and execute the attacker-controlled code within the Arelle process with its privileges.

Severity
critical
Software
Python
Fixed in
2.39.10
Published
2026-05-04

Affected versions

Until: 2.39.10

Fixed in: 2.39.10

How to fix this CVE

Upgrade Arelle to version 2.39.10 or later to patch the unauthenticated remote code execution vulnerability in the REST /configure endpoint. This vulnerability allows attackers to execute arbitrary Python code by supplying a malicious plugin URL without authentication. Immediately update your Python environment and verify the patched Arelle version is deployed in production.

sudo dnf update arelle python3-arelle

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET /rest/configure.*[?&]plugins=https?://.*\.(py|zip|tar|gz) HTTP

WAF mitigation (if patching is not yet possible)

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

Block all unauthenticated requests to /rest/configure endpoint. Implement IP whitelisting for REST API access and require HTTP Basic Authentication or API token headers on all /rest/* paths. Consider blocking plugin parameter values containing http:// or https:// URLs.

How to check if you are affected

  1. Check the installed Arelle version: arelle --version or python3 -c "import arelle; print(arelle.__version__)"
  2. Verify the REST API endpoint is exposed: curl -s http://localhost:8080/rest/configure | head -20
  3. Search web server logs for /rest/configure requests with 'plugins' parameter: grep -r 'rest/configure.*plugins' /var/log/apache2/ /var/log/nginx/ /var/log/httpd/
  4. Confirm the fix by checking that Arelle version >= 2.39.10 is running: pip3 show arelle | grep Version

FAQ

What is CVE-2026-42796?

This is a critical unauthenticated remote code execution vulnerability in Arelle's REST /configure endpoint. An attacker can inject a malicious Python plugin URL via the 'plugins' parameter, causing the Arelle webserver to download and execute arbitrary code with the privileges of the Arelle process.

Is CVE-2026-42796 being actively exploited?

No, this vulnerability is not currently listed in the CISA KEV catalog and has no known public exploits available, though the attack method is straightforward and exploitation should be anticipated.

What versions of Arelle are affected by CVE-2026-42796?

All versions of Arelle prior to 2.39.10 are vulnerable. Version 2.39.10 and later contain the security patch that removes unauthenticated access to the plugin configuration endpoint.

How do I check if my server is vulnerable to CVE-2026-42796?

Run 'python3 -c "import arelle; print(arelle.__version__)"' and verify the version is 2.39.10 or higher. Additionally, attempt a test query to the /rest/configure endpoint without credentials to confirm it is accessible.

Does Defensia detect CVE-2026-42796?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Arelle or Python is installed on a monitored server, CVE-2026-42796 will appear in your dashboard with remediation steps.

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References

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