{"id":"CVE-2026-117553","state":"PUBLISHED","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.","publishedAt":"2026-10-27T13:07:49.671Z","updatedAt":"2026-10-27T13:07:49.671Z","severity":{"score":7.7,"label":"High","version":"4.0","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","source":"VulnCheck"},"assigner":"VulnCheck","products":["umbraco Umbraco-CMS"],"affected":[{"vendor":"umbraco","product":"Umbraco-CMS","packageURL":"pkg:nuget/Umbraco.Cms","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"17.7.2","versionType":"semver"},{"version":"18.0.0","status":"affected","lessThan":"18.2.2","versionType":"semver"}]}],"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"],"weaknesses":["CWE-601"],"ingestedAt":"2026-10-29T20:10:52.580Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/117xxx/CVE-2026-117553.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-117553","state":"PUBLISHED","datePublished":"2026-10-27T13:07:49.671Z","dateUpdated":"2026-10-27T13:07:49.671Z","assignerShortName":"VulnCheck","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","dateReserved":"2026-10-27T11:25:13.186Z"},"containers":{"cna":{"title":"Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning","descriptions":[{"lang":"en","value":"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. 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