zrok: Reflected XSS in GitHub OAuth callback via unsanitized refreshInterval error rendering

**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() / WriteTemplate (lines 8, 18, 99) — text/template used for HTML rendering - endpoints/proxyUi/template.html — line 119 — {{ .Error }} in HTML without escaping - endpoints/publicProxy/providerGithub.go — login callback closure (lines 93, 128, 130) - endpoints/dynamicProxy/providerGithub.go — loginHandler() (lines 110, 146, 148)

Source published

16 Apr 2026 21:08:55 UTC

Source modified

25 Jun 2026 18:56:29 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Publisher rating · MODERATE