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CVE-2026-27734: Beszel Vulnerable to Docker API Path Traversal via Unsanitized Container ID

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-02-27 · updated 2026-06-17
• Weakness: CWE-22

Description

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.

Affected products

• henrygd beszel: before 0.18.2 — fixed in 0.18.2

How to fix

Upgrade to a fixed version: henrygd beszel 0.18.2. Check the vendor advisory for mitigations.

References

• https://github.com/henrygd/beszel/releases/tag/v0.18.4
• https://github.com/henrygd/beszel/security/advisories/GHSA-phwh-4f42-gwf3

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