high CVSS 7.2

CVE-2026-40242·Docker vulnerability

Arcane is an interface for managing Docker containers, images, networks, and volumes. Prior to 1.17.3, the /api/templates/fetch endpoint accepts a caller-supplied url parameter and performs a server-side HTTP GET request to that URL without authentication and without URL scheme or host validation. The server's response is returned directly to the caller. type. This constitutes an unauthenticated SSRF vulnerability affecting any publicly reachable Arcane instance. This vulnerability is fixed in 1.17.3.

Severity
high
Software
Docker
Fixed in
1.17.3
Published
2026-04-10

Affected versions

Until: 1.17.3

Fixed in: 1.17.3

How to fix this CVE

Upgrade Arcane to version 1.17.3 or later to patch an unauthenticated server-side request forgery (SSRF) vulnerability in the /api/templates/fetch endpoint. This vulnerability allows attackers to make arbitrary HTTP requests from the server without authentication, potentially exposing internal services or sensitive data. Apply the update immediately if you run Arcane in a publicly accessible environment.

sudo dnf update docker-ce

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET /api/templates/fetch\?url=(?!https?:\/\/([a-zA-Z0-9-]+\.)*yourdomain\.com)[^\s]+ HTTP\/1\.[01]|url parameter containing internal IP patterns (127\.0\.0\.1|10\.\d{1,3}|172\.1[6-9]\.|172\.2[0-9]\.|172\.3[01]\.|192\.168\.|localhost|169\.254)

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 /api/templates/fetch with url parameters that resolve to RFC 1918 private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), 127.0.0.1, ::1, or link-local addresses; whitelist only approved external domains if the endpoint must remain public; require authentication headers before allowing access to any /api/templates/* endpoints.

How to check if you are affected

  1. Run `docker --version` and `docker info` to confirm the installed version of Docker and check for any Arcane container images running.
  2. Execute `docker ps --all --filter 'ancestor=*arcane*'` to identify if Arcane containers are deployed; note their image tags to determine if versions prior to 1.17.3 are in use.
  3. Search application logs for requests to `/api/templates/fetch` endpoint with suspicious `url` parameters (e.g., `http://127.0.0.1`, `http://localhost`, or internal IP ranges) using: `grep -i 'templates/fetch' /var/log/docker/*.log | grep -E '(127\.0\.0\.1|localhost|10\.|172\.|192\.)'`
  4. Verify the patched version is running by inspecting the container image metadata: `docker inspect <arcane-container-id> | grep -i version` or check the Arcane application dashboard for version 1.17.3 or higher.

FAQ

What is CVE-2026-40242?

CVE-2026-40242 is an unauthenticated server-side request forgery (SSRF) vulnerability in Arcane's /api/templates/fetch endpoint that allows remote attackers to make arbitrary HTTP requests from the server without validation, potentially accessing internal services or exfiltrating sensitive data.

Is CVE-2026-40242 being actively exploited?

No, this vulnerability is not currently listed in CISA's Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available; however, the attack vector is network-based with no authentication required, making it a high-priority patch for publicly exposed instances.

What versions of Docker are affected by CVE-2026-40242?

The vulnerability affects Arcane (a Docker management interface) versions prior to 1.17.3. While the CVE references Docker, the specific vulnerability is in the Arcane application layer, so all Arcane deployments on versions before 1.17.3 are at risk.

How do I check if my server is vulnerable to CVE-2026-40242?

Run `docker inspect <container-id> --format='{{.Config.Image}}'` to identify Arcane containers, then check the image tag against version 1.17.3; alternatively, query the Arcane application's version endpoint if exposed, or examine container build metadata with `docker history <image-id>`.

Does Defensia detect CVE-2026-40242?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Docker or Arcane is installed on a monitored server, CVE-2026-40242 will appear in your dashboard with remediation steps.

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References

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