medium CVSS 6.5 EPSS <0.1%

CVE-2026-27734·Docker vulnerability

Beszel is a server monitoring platform. Prior to version 0.18.2, the hub's authenticated API endpoints GET /api/beszel/containers/logs and GET /api/beszel/containers/info pass the user-supplied "container" query parameter to the agent without validation. The agent constructs Docker Engine API URLs using fmt.Sprintf with the raw value instead of url.PathEscape(). Since Go's http.Client does not sanitize `../` sequences from URL paths sent over unix sockets, an authenticated user (including readonly role) can traverse to arbitrary Docker API endpoints on agent hosts, exposing sensitive infrastructure details. Version 0.18.4 fixes the issue.

Severity
medium
Software
Docker
Fixed in
0.18.2
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 3% 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: 0.18.2

Fixed in: 0.18.2

How to fix this CVE

Update Docker to version 0.18.4 or later to patch a path traversal vulnerability in the Beszel monitoring platform that allows authenticated users to bypass API endpoint restrictions. This vulnerability affects Docker installations used with Beszel monitoring agents running on the same host. Apply the update immediately across all affected infrastructure to prevent unauthorized access to Docker API endpoints.

sudo dnf update docker-ce docker-ce-cli docker-buildx-plugin docker-compose-plugin

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET /api/beszel/containers/(logs|info)\?container=\.\.%2F(images|networks|containers|volumes) or similar URL-encoded path traversal sequences in Beszel hub API requests from authenticated users

WAF mitigation (if patching is not yet possible)

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

Implement input validation rules to reject container parameter values containing '..', '/', '%2f', '%2e', or other path traversal indicators before they reach the Docker agent; enforce allowlist matching against valid container ID/name patterns (alphanumeric, dash, underscore only)

How to check if you are affected

  1. Run 'docker --version' and check if the version is 0.18.2 or earlier; if Beszel is deployed, verify the hub version with 'curl http://localhost:8090/api/version' (adjust URL for your environment)
  2. Check if Beszel hub API endpoints are exposed to the network by reviewing Docker port mappings: 'docker ps | grep beszel'
  3. Search Docker daemon logs for suspicious container API calls: 'docker logs <container-id> | grep -i '../' or 'docker logs <container-id> | grep -E '(containers|images|networks)' | grep -v standard'
  4. Verify the patch by confirming Beszel version is 0.18.4+: check the release tag in your deployment or inspect the container image digest against the official Beszel repository

FAQ

What is CVE-2026-27734?

CVE-2026-27734 is a path traversal vulnerability in Beszel's Docker API integration where user-supplied container query parameters are not properly escaped when constructing Docker API URLs, allowing authenticated users to access arbitrary Docker endpoints and retrieve sensitive infrastructure information.

Is CVE-2026-27734 being actively exploited?

No, this vulnerability is not listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are currently available, though it remains a significant risk for Beszel deployments with network-exposed hub instances.

What versions of Docker are affected by CVE-2026-27734?

The vulnerability affects Beszel versions prior to 0.18.4; Docker itself is not directly vulnerable, but Docker installations monitoring agents communicating with vulnerable Beszel hub instances are at risk of unauthorized API access.

How do I check if my server is vulnerable to CVE-2026-27734?

Run 'docker exec <beszel-hub-container> cat /app/version.txt' or check your Beszel deployment logs for version information; if the version is 0.18.2 or earlier, your installation is vulnerable.

Does Defensia detect CVE-2026-27734?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Docker is installed on a monitored server, CVE-2026-27734 will appear in your dashboard with remediation steps.

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References

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