medium CVSS 5.9 EPSS 0.27%

CVE-2026-55761·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. In versions 2.39.0 through 2.39.3 and 2.40.0 until 2.43.0, unauthenticated restore and administrator initialization endpoints (/api/restore and /api/users/admin/init) remain accessible during the five-minute setup window for uninitialized instances, allowing a network attacker to restore a crafted backup or create the first administrator account and gain full administrative access. This issue is fixed in versions 2.39.4 and 2.43.0.

Severity
medium
Software
Docker
Fixed in
2.43.0
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 0.27% — higher than 19% 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

From: 2.40.0

Until: 2.43.0

Fixed in: 2.43.0

How to fix this CVE

Update Docker to version 2.43.0 or later to patch the unauthenticated initialization vulnerability. During the five-minute setup window on fresh instances, ensure network access to administrative endpoints is restricted until initialization is complete. If you cannot update immediately, implement network-level controls to block access to /api/restore and /api/users/admin/init endpoints from untrusted sources.

sudo dnf update docker-ce

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST /api/restore HTTP/1.1|POST /api/users/admin/init HTTP/1.1|"endpoint":"/api/restore"|"endpoint":"/api/users/admin/init"

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 /api/restore and /api/users/admin/init endpoints by implementing authentication checks before these routes are processed. Use WAF rules to deny POST/GET requests matching these paths unless they include valid authentication tokens or come from whitelisted internal IPs.

How to check if you are affected

  1. Run 'docker --version' or 'docker version' to check the installed Docker version and confirm if it falls within the vulnerable range (2.40.0 to 2.43.0).
  2. Check if your Docker instance has been initialized by verifying the presence of admin user accounts with 'docker exec <container-id> curl -s http://localhost:9000/api/users | grep admin' if running Portainer in a container.
  3. Review Docker daemon and application logs for POST requests to /api/restore or /api/users/admin/init from unexpected sources: 'grep -i "api/restore\|api/users/admin/init" /var/log/docker* /var/log/containers/* 2>/dev/null'.
  4. Verify the patch was applied by confirming the Docker version is 2.43.0 or later and checking commit hashes in 'docker inspect <image-id>' to ensure the vulnerable code has been removed.

FAQ

What is CVE-2026-55761?

CVE-2026-55761 is an authentication bypass vulnerability in Docker's initialization endpoints that allows an unauthenticated attacker to restore a malicious backup or create an administrator account during the five-minute setup window of a fresh instance, leading to full system compromise.

Is CVE-2026-55761 being actively exploited?

No, according to CISA's Known Exploited Vulnerabilities (KEV) catalog, CVE-2026-55761 is not currently being actively exploited in the wild, and no public exploit code is available.

What versions of Docker are affected by CVE-2026-55761?

Docker versions 2.40.0 through 2.43.0 are affected; versions 2.39.4 and 2.43.0+ contain the patch.

How do I check if my server is vulnerable to CVE-2026-55761?

Run 'docker --version' and verify the version is between 2.40.0 and 2.43.0. Additionally, check if unauthenticated access to the /api/restore endpoint is possible with: 'curl -s -X GET http://localhost:9000/api/restore' — a successful response indicates vulnerability.

Does Defensia detect CVE-2026-55761?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Docker is installed on a monitored server, CVE-2026-55761 will appear in your dashboard with remediation steps.

Related Docker CVEs

CVE-2026-42298CVSS 10Postiz is an AI social media scheduling tool. Prior to commit da44801, a "Pwn Request" vulnerability in the Build and Publish PR Docker Image workflow (.github/workflows/pr-docker-build.yml) allows any unauthenticated user to execute arbitrary code during the Docker build process and exfiltrate a highly privileged GITHUB_TOKEN (write-all permissions). This can be achieved simply by opening a Pull Request from a fork with a maliciously modified Dockerfile.dev. This issue has been patched via commit da44801.
CVE-2026-57572CVSS 10Crawl4AI is an open-source LLM-friendly web crawler and scraper. Prior to 0.9.0, the Docker API server accepted request-supplied browser_config.extra_args, which flowed into Chromium's launch arguments. An attacker could inject Chromium switches that replace a child-process launch command together with --no-zygote, causing Chromium to fork or exec an attacker-controlled command as the container's runtime user. The Docker API is unauthenticated by default, so a single request yields arbitrary command execution. This issue is fixed in version 0.9.0.
CVE-2026-44182CVSS 10Jupyter Enterprise Gateway launches remote Jupyter Notebook kernels across distributed clusters like Apache Spark, Kubernetes, and Docker Swarm. In versions prior to 3.3.0, the server interpolates untrusted environment variables (e.g., KERNEL_XXX) into Kubernetes manifests without YAML-aware escaping, enabling YAML injection attacks. Attackers can inject new fields, overwrite critical fields (e.g., duplicate securityContext keys, where the last one prevails), and inject document boundaries (--- for new documents, ... for end-of-document) to generate multiple resources, potentially creating arbitrary types, such as privileged pods. The Jinja2 template for the Kubernetes manifest contains several kernel_xxx variables, such as kernel_working_dir that are used when rendering the manifest and are all vectors for YAML injection. This issue has been fixed in version 3.3.0.
CVE-2026-44181CVSS 10Jupyter Enterprise Gateway launches remote Jupyter Notebook kernels across distributed clusters like Apache Spark, Kubernetes, and Docker Swarm. In versions 2.0.0rc2 and above, prior to 3.3.0, the environment variables (KERNEL_XXX) used during the rendering of the Kubernetes manifest are vulnerable to Server Side Template Injection (SSTI). By including Jinja2 template expressions it is possible to execution Python code and OS Commands in the Enterprise Gateway service. The code can use or steal the Kubernetes service account token, which can steal Kubernetes secrets and be used to fully compromise the Kubernetes cluster by scheduling a privileged pod or a pod with a hostPath volume mount. This issue has been fixed in version 3.3.0.
CVE-2026-53576CVSS 10Kestra is an open-source, event-driven orchestration platform. Prior to 1.0.45 and 1.3.21, the authentication filter for the REST API (@Filter("/api/v1/**")) treats any request whose path ends in /configs as the public instance-config endpoint and forwards it without a credential check. kestra addresses its resources by URL path segments that the caller chooses (/api/v1/{tenant}/flows/{namespace}, /api/v1/{tenant}/executions/{namespace}/{id}, /api/v1/{tenant}/namespaces/{namespace}/kv/{key}). An anonymous caller picks the literal configs as the final segment, and the request bypasses Basic-Auth entirely. Because the bypass reaches the flow-create and execution-trigger routes, an unauthenticated caller creates a flow containing a Shell or Process task and runs it. The task executes as root inside the kestra container. The official docker-compose.yml mounts /var/run/docker.sock, so root in the container reaches the host Docker daemon. This vulnerability is fixed in 1.0.45 and 1.3.21.

References

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2026-55761. Free for 1 server.

Get started free