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CVE-2026-117553 Details

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.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:7.5 HIGHVector:CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/umbraco/Umbraco-CMS	[email protected]
https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112	[email protected]
https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6	[email protected]
https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469	[email protected]
https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning	[email protected]

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-601	URL Redirection to Untrusted Site ('Open Redirect')	[email protected]

Affected Products

No affected product data is available for this CVE.

Change History

2 change records found show changes

Date	Action	Recorded By
Nov 4, 2026	CVE Modified	CISA-ADP
Oct 27, 2026	New CVE Received	[email protected]