Beszel: Docker API has a Path Traversal Vulnerability via Unsanitized Container ID

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-27734: 0.55% estimated exploitation activity in the next 30 days; percentile 45.77 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details Hub (internal/hub/hub.go:407-426): containerID from query param is only checked for emptiness, no format validation: Agent (agent/docker.go:651-652 and 682-683): raw containerID interpolated into Docker API URL: Go's http.Client preserves ../ in paths over unix sockets (verified with test code). The Docker daemon resolves them via cleanPath, routing the request to unintended API endpoints. PoC Tested on Beszel v0.18.3 with hub and…

Published by the source

27 Feb 2026, 21:01 UTC

Last modified by the source

27 Feb 2026, 22:20 UTC

Source last checked

26 Oct 2026, 15:14 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-phwh-4f42-gwf3

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# Patch Next advisory brief: CVE-2026-27734

Advisory: Beszel: Docker API has a Path Traversal Vulnerability via Unsanitized Container ID
IDs: CVE-2026-27734, GHSA-phwh-4f42-gwf3
Record: https://patchnext.com/advisories/cve-2026-27734 (revision 1, source checked 26 Oct 2026, 15:14 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/henrygd/beszel 0.18.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/henrygd/beszel: affected <= 0.18.3; fixed in 0.18.4

## Suggested inspection (read-only)
- Go github.com/henrygd/beszel: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/henrygd/beszel.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-phwh-4f42-gwf3 (GitHub-reviewed advisory GHSA-phwh-4f42-gwf3 lists affected ranges: Go github.com/henrygd/beszel >=0 <=0.18.3)

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