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.

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History

Tue, 27 Oct 2026 13:45:00 +0000

Type Values Removed Values Added
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.
Title Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning
First Time appeared Umbraco
Umbraco umbraco Cms
Weaknesses CWE-601
CPEs cpe:2.3:a:umbraco:umbraco_cms:*:*:*:*:*:*:*:*
Vendors & Products Umbraco
Umbraco umbraco Cms
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H'}

cvssV4_0

{'score': 7.7, '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'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-10-27T13:07:49.671Z

Reserved: 2026-10-27T11:25:13.186Z

Link: CVE-2026-117553

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-27T14:16:35.840

Modified: 2026-10-27T16:03:45.247

Link: CVE-2026-117553

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-27T16:15:04Z

Weaknesses