{"affected":[{"defaultStatus":"unaffected","ecosystem":"nuget","packageName":"Umbraco.Cms","product":"Umbraco-CMS","source":"CNA: VulnCheck","vendor":"umbraco","versions":[{"lessThan":"17.7.2","status":"affected","version":"0","versionType":"semver"},{"lessThan":"18.2.2","status":"affected","version":"18.0.0","versionType":"semver"}]}],"cveId":"CVE-2026-117553","cwes":["CWE-601"],"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.","epss":{"date":"2026-11-04","percentile":0.42625,"score":0.00495},"exploits":[],"kev":null,"metrics":[{"score":7.7,"severity":"high","source":"CNA: VulnCheck","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","version":"4.0"},{"score":7.5,"severity":"high","source":"CNA: VulnCheck","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","version":"3.1"},{"score":7.7,"severity":"high","source":"NVD: disclosure@vulncheck.com","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","version":"4.0"},{"score":7.5,"severity":"high","source":"NVD: disclosure@vulncheck.com","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","version":"3.1"}],"modifiedAt":1793809064097,"publishedAt":1793106469671,"references":[{"source":"CNA: VulnCheck","tags":["patch"],"url":"https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6"},{"source":"CNA: VulnCheck","tags":["product"],"url":"https://github.com/umbraco/Umbraco-CMS"},{"source":"CNA: VulnCheck","tags":["vendor-advisory"],"url":"https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469"},{"source":"CNA: VulnCheck","tags":["technical-description"],"url":"https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112"},{"source":"CNA: VulnCheck","tags":["third-party-advisory"],"url":"https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/umbraco/Umbraco-CMS"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning"}],"remediation":[{"kind":"fix","source":"CNA: VulnCheck","text":"The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.","url":"https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6"}],"revision":"b97deb74df40025d9fbe29a2d0e1d6bda714a1377569eeb7b55c49faffb7c708","sources":[{"modifiedAt":1793807796930,"name":"CNA: VulnCheck","retrievedAt":1793808600625,"url":"https://www.cve.org/CVERecord?id=CVE-2026-117553"},{"modifiedAt":1793809064097,"name":"NVD","retrievedAt":1793816542088,"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-117553"},{"modifiedAt":null,"name":"FIRST EPSS","retrievedAt":1793808631334,"url":"https://api.first.org/data/v1/epss?cve=CVE-2026-117553"}],"ssvc":{"assessedAt":1793807788268,"automatable":"no","exploitation":"none","source":"ADP: CISA-ADP","technicalImpact":"total"},"status":"published","title":"Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning","updatedAt":1793816542088}