zrok: Reflected XSS in GitHub OAuth callback via unsanitized refreshInterval error rendering
Date: 2026-04
Affected: go/github.com/openziti/zrok/v2, go/github.com/openziti/zrok
Attack vector: xss
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-40302
CWE: CWE-116
CWE-79
CVSS: 6.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N)

**Summary** The proxyUi template engine uses Go's text/template (which performs no HTML escaping) instead of html/template. The GitHub OAuth callback handlers in both publicProxy and dynamicProxy embed the attacker-controlled refreshInterval query parameter verbatim into an error message when time.ParseDuration fails, and render that error unescaped into HTML. An attacker can deliver a crafted login URL to a victim; after the victim completes the GitHub OAuth flow, the callback page executes arbitrary JavaScript in the OAuth server's origin. - Attack Vector: Network — the attack is delivered as a crafted URL over the internet. - Attack Complexity: Low — no race conditions or special environment prerequisites. - Privileges Required: None — the attacker needs no account on the zrok instance. - User Interaction: Required — the victim must click the crafted link and complete the GitHub OAuth flow. - Scope: Changed — the injected script executes in the OAuth server's origin, not the victim's share origin. - Confidentiality Impact: Low — the script runs in the OAuth server origin after a failed flow; no session cookie is set at this point, limiting what can be exfiltrated to what is visible in the DOM and what can be requested from the OAuth server. - Integrity Impact: Low — the script can initiate new OAuth flows or submit forms on behalf of the victim in the OAuth server origin. - Availability Impact: None. **Affected Components** - endpoints/proxyUi/template.go — init() / Wri


Mitigations:

Architectural layers (MAESTRO):