{"id":"CVE-2026-40302","aliases":["GHSA-4fxq-2x3x-6xqx","GO-2026-5118"],"url":"https://o3.security/vulnerability/CVE-2026-40302","summary":"zrok has 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)","published":"2026-04-17T20:56:08.368Z","modified":"2026-08-12T03:51:10.856064696Z","cvss":{"score":6.1,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"},"epss":{"score":0.00209,"percentile":0.11143,"asOf":"2026-08-10"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/openziti/zrok","fixedVersion":null},{"ecosystem":"Go","name":"github.com/openziti/zrok/v2","fixedVersion":"2.0.1"}],"fix":null,"references":[{"type":"WEB","url":"https://github.com/openziti/zrok/releases/tag/v2.0.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40302.json"},{"type":"ADVISORY","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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:10.856064696Z"}}