CVE-2026-40302: zrok Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-4fxq-2x3x-6xqx",
  "modified" : "2026-04-24T20:48:45Z",
  "published" : "2026-04-16T21:08:55Z",
  "aliases" : [ "CVE-2026-40302" ],
  "summary" : "zrok: Reflected XSS in GitHub OAuth callback via unsanitized refreshInterval error rendering",
  "details" : "**Summary**\nThe 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.\n\n- Attack Vector: Network — the attack is delivered as a crafted URL over the internet.\n- Attack Complexity: Low — no race conditions or special environment prerequisites.\n- Privileges Required: None — the attacker needs no account on the zrok instance.\n- User Interaction: Required — the victim must click the crafted link and complete the GitHub OAuth flow.\n- Scope: Changed — the injected script executes in the OAuth server's origin, not the victim's share origin.\n- 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.\n- Integrity Impact: Low — the script can initiate new OAuth flows or submit forms on behalf of the victim in the OAuth server origin.\n- Availability Impact: None.\n\n**Affected Components**\n\n- endpoints/proxyUi/template.go — init() / WriteTemplate (lines 8, 18, 99) — text/template used for HTML rendering\n- endpoints/proxyUi/template.html — line 119 — {{ .Error }} in HTML without escaping\n- endpoints/publicProxy/providerGithub.go — login callback closure (lines 93, 128, 130)\n- endpoints/dynamicProxy/providerGithub.go — loginHandler() (lines 110, 146, 148)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/openziti/zrok"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "1.1.11"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/openziti/zrok/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.0.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/openziti/zrok/security/advisories/GHSA-4fxq-2x3x-6xqx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40302"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/openziti/zrok"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/openziti/zrok/releases/tag/v2.0.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-116", "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-16T21:08:55Z",
    "nvd_published_at" : "2026-04-17T21:16:34Z"
  }
}