medium CVSS 6.5

CVE-2026-44884·Docker vulnerability

Portainer Community Edition is a lightweight service delivery platform for containerized applications that can be used to manage Docker, Swarm, Kubernetes and ACI environments. From 2.33.0 to before 2.33.8 and 2.39.1, a missing authorization vulnerability in the Custom Template file endpoint (GET /api/custom_templates/{id}/file) allows any authenticated user to read the file content of any custom template by enumerating sequential integer IDs, bypassing Resource Control access restrictions. Template files may contain environment-specific values such as connection strings, API tokens, or registry credentials that administrators would not expect standard users to read. This vulnerability is fixed in 2.33.8 and 2.39.1.

Severity
medium
Software
Docker
Fixed in
2.39.1
Published
2026-05-28

Affected versions

From: 2.39.0

Until: 2.39.1

Fixed in: 2.39.1

How to fix this CVE

Update Docker to the patched version immediately to close the Custom Template file access vulnerability in Portainer. Users running Portainer 2.39.0 should upgrade to 2.39.1 or later. Audit any custom templates that may contain sensitive credentials, connection strings, or API tokens, as unauthorized users could have enumerated and accessed their contents.

sudo dnf update docker-ce

Defensia detects this vulnerability

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 restrict unauthenticated or low-privilege user access to /api/custom_templates/* endpoints; require role-based authorization checks before returning template file content and log all requests to this endpoint for audit purposes.

How to check if you are affected

  1. Run 'docker --version' and cross-reference against Portainer release notes to confirm your Portainer version is 2.39.1 or later
  2. Check the Portainer container logs with 'docker logs <portainer_container_id>' for any authentication-related errors or suspicious API requests to /api/custom_templates/{id}/file endpoints
  3. Query your Docker daemon logs for unauthorized or repeated GET requests to the Custom Template file endpoint: 'docker logs <portainer_container_id> | grep -i custom_templates'
  4. Verify the fix by examining your Portainer instance settings or admin panel to confirm the running version matches the patched release (2.39.1 or 2.33.8+)

FAQ

What is CVE-2026-44884?

This is a missing authorization flaw in Portainer's Custom Template file endpoint that allows any authenticated user to access sensitive template files (containing credentials, API tokens, or connection strings) by sequentially guessing template IDs, regardless of their assigned access control permissions.

Is CVE-2026-44884 being actively exploited?

No, this vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog, and no public exploits are currently available.

What versions of Docker are affected by CVE-2026-44884?

Portainer Community Edition versions 2.39.0 to 2.39.0 (and earlier versions 2.33.0 through 2.33.7) are vulnerable. The fix is available in Portainer 2.39.1 and 2.33.8.

How do I check if my server is vulnerable to CVE-2026-44884?

Run 'docker exec <portainer_container_id> /portainer -v' or check your Portainer admin dashboard under Settings > About to identify the installed version; if it is 2.39.0 or earlier (within the affected range), you are vulnerable.

Does Defensia detect CVE-2026-44884?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Docker and Portainer are installed on a monitored server, CVE-2026-44884 will appear in your dashboard with remediation steps.

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References

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