CVE-2026-40304 — zrok
MEDIUMCVE-2026-40304 is a medium-severity (CVSS 5.3) vulnerability in github.com/openziti/zrok. A fix is available for github.com/openziti/zrok — see the affected versions and patch details below.
zrok's broken ownership check in DELETE /api/v2/unaccess allows non-admin to delete global frontend records
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-2026-40304.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-40304 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/openziti/zrok🐹github.com/openziti/zrok/v2Real-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 unaccess handler (controller/unaccess.go) contains a logical error in its ownership guard: when a frontend record has environment_id = NULL (the marker for admin-created global frontends), the condition short-circuits to false and allows the deletion to proceed without any ownership verification. A non-admin user who knows a global frontend token can call DELETE /api/v2/unaccess with any of their own environment IDs and permanently delete the global frontend, taking down all public shares routed through it.
Attack Vector: Network — the endpoint is a standard HTTP API call.
Attack Complexity: High — successful exploitation requires prior knowledge of a global frontend token. These tokens are not returned to non-admin users by any standard API endpoint; obtaining one requires an out-of-band step (e.g., leaked server logs, admin documentation for a self-hosted instance, or social engineering).
Privileges Required: Low — a valid user account with at least one registered environment is required; no admin privileges needed.
User Interaction: None.
Scope: Unchanged — the impact stays within the same server instance.
Confidentiality Impact: None — no data is disclosed.
Integrity Impact: None — no data is improperly modified; the record is deleted (not corrupted).
Availability Impact: High — deleting a global frontend disrupts every public share routed through it on the instance, constituting a platform-wide availability impact.
Affected Component controller/unaccess.go — unaccessHandler.Handle (line 56)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/openziti/zrok | all versions | No fix |
| 🐹Go | github.com/openziti/zrok/v2 | all versions | 2.0.1go get github.com/openziti/zrok/v2@v2.0.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/openziti/zrok, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
No patched version of github.com/openziti/zrok has shipped for CVE-2026-40304 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-40304 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-40304. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-40304 in your dependencies?
O3 Security finds CVE-2026-40304 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.