{"id":"CVE-2026-117553","aliases":["GHSA-rpv9-qp4c-g469"],"url":"https://o3.security/vulnerability/CVE-2026-117553","summary":"Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning","details":"Umbraco CMS before 17.7.2 and 18.2.2 contains an authentication bypass vulnerability that allows unauthenticated attackers to register attacker-controlled OAuth redirect URIs by poisoning the Host header. Attackers send signed-in users authorization links using response_mode=form_post to capture codes, then redeem them via HTTP Basic client credentials to hijack back-office sessions and execute code through Razor templates.","published":"2026-10-27T13:07:49.671Z","modified":"2026-10-28T02:56:19.633381677Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[],"fix":{"url":"https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6","label":"umbraco/Umbraco-CMS@490b9b2"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/117xxx/CVE-2026-117553.json"},{"type":"PACKAGE","url":"https://github.com/umbraco/Umbraco-CMS"},{"type":"ARTICLE","url":"https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112"},{"type":"FIX","url":"https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6"},{"type":"ADVISORY","url":"https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-117553"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:56:19.633381677Z"}}