{"id":"CVE-2026-117553","published":"2026-10-27T14:16:35.840","lastModified":"2026-10-27T16:03:45.247","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.","cvssScore":7.5,"cvssSeverity":"HIGH","cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","cwes":["CWE-601"],"vendors":[],"products":[],"references":[{"url":"https://github.com/umbraco/Umbraco-CMS","tags":[]},{"url":"https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112","tags":[]},{"url":"https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6","tags":[]},{"url":"https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469","tags":[]},{"url":"https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning","tags":[]}],"exploitRefs":[{"url":"https://github.com/umbraco/Umbraco-CMS","tags":[]},{"url":"https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112","tags":[]},{"url":"https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6","tags":[]},{"url":"https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469","tags":[]}],"hasPoc":true,"ai":null}