{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-117553", "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "state": "PUBLISHED", "assignerShortName": "VulnCheck", "dateReserved": "2026-10-27T11:25:13.186Z", "datePublished": "2026-10-27T13:07:49.671Z", "dateUpdated": "2026-10-27T13:07:49.671Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "shortName": "VulnCheck", "dateUpdated": "2026-10-27T13:07:49.671Z"}, "datePublic": "2026-10-27T00:00:00.000Z", "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. 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."}], "problemTypes": [{"descriptions": [{"lang": "en", "description": "URL Redirection to Untrusted Site ('Open Redirect')", "cweId": "CWE-601", "type": "CWE"}]}], "affected": [{"vendor": "umbraco", "product": "Umbraco-CMS", "defaultStatus": "unaffected", "versions": [{"status": "affected", "version": "0", "lessThan": "17.7.2", "versionType": "semver"}, {"status": "affected", "version": "18.0.0", "lessThan": "18.2.2", "versionType": "semver"}], "packageURL": "pkg:nuget/Umbraco.Cms"}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:umbraco:umbraco_cms:*:*:*:*:*:*:*:*", "versionEndExcluding": "17.7.2"}, {"vulnerable": true, "criteria": "cpe:2.3:a:umbraco:umbraco_cms:*:*:*:*:*:*:*:*", "versionStartIncluding": "18.0.0", "versionEndExcluding": "18.2.2"}]}]}], "metrics": [{"format": "CVSS", "cvssV4_0": {"version": "4.0", "vectorString": "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", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "PASSIVE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "baseScore": 7.7, "baseSeverity": "HIGH"}}, {"format": "CVSS", "cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH"}}], "references": [{"url": "https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6", "tags": ["patch"], "name": "Patch Commit"}, {"url": "https://github.com/umbraco/Umbraco-CMS", "tags": ["product"]}, {"url": "https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469", "tags": ["vendor-advisory"], "name": "GitHub Security Advisory (GHSA-rpv9-qp4c-g469)"}, {"url": "https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112", "tags": ["technical-description"]}, {"name": "VulnCheck Advisory: Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning", "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"}], "credits": [{"lang": "en", "value": "Eu Joe Chegne (Project Umbra)", "type": "finder"}, {"lang": "en", "value": "Damien Wong (Project Umbra)", "type": "finder"}, {"lang": "en", "value": "AndyButland", "type": "remediation developer"}], "x_generator": {"engine": "vulncheck-endgame"}}}}

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{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,17.7.2)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[18.0.0,18.2.2)"}}], "enrichment": {"confidence": 90.0, "confidence_source": "inferred", "scores": [{"score": 90.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Umbraco-CMS", "source": "cna", "vendor": "umbraco"}, "product": "umbraco_cms", "vendor": "umbraco"}], "created": "2026-10-27T14:30:04.722804+00:00", "updated": "2026-10-27T16:15:04.525967+00:00", "vendors": ["umbraco", "umbraco$PRODUCT$umbraco_cms"]}