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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.","state":0,"publishedAt":"2026-10-27T13:07:49.671+00:00","modifiedAt":"2026-10-27T13:07:49.671+00:00","affected":[{"ecosystem":"NuGet","name":"Umbraco.Cms","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"umbraco\",\n                    \"product\": \"Umbraco-CMS\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"0\",\n                            \"lessThan\": \"17.7.2\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"18.0.0\",\n                            \"lessThan\": \"18.2.2\",\n                            \"versionType\": \"semver\"\n                        }\n                    ],\n                    \"packageURL\": \"pkg:nuget/Umbraco.Cms\"\n                }"}],"metrics":[{"system":"CVSS 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","score":7.7,"severity":"HIGH"},{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","score":7.5,"severity":"HIGH"}],"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"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-117553","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-117553","identifiers":["CVE-2026-117553"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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