{"id":"CVE-2026-117553","aliases":[],"title":"Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning","description":"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templates.","severity":"high","score":7.7,"published":"2026-10-27T13:07:49.671Z","modified":"2026-10-27T13:07:49.671Z","withdrawn":false,"knownExploited":false,"affected":[],"references":["https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6","https://github.com/umbraco/Umbraco-CMS","https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469","https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112","https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning"],"sources":[{"name":"CVE","id":"CVE-2026-117553","modified":"2026-10-27T13:07:49.671Z","url":"https://www.cve.org/CVERecord?id=CVE-2026-117553"}],"assessments":[{"source":"CNA","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","score":7.7},{"source":"CNA","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","score":7.5}]}