CVE-2026-117553
Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-601 |
| Vendor | umbraco |
| Product | umbraco-cms |
| Published | Oct 27, 2026 |
Stay Ahead of the Next One
Get instant alerts for umbraco umbraco-cms
Be the first to know when new high vulnerabilities affecting umbraco umbraco-cms are published — delivered to Slack, Telegram or Discord.
Get Free Alerts →
Free · No credit card · 60 sec setup
CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Affected Versions
umbraco / Umbraco-CMS
0 < 17.7.2 18.0.0 < 18.2.2
References
github.com: https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6 github.com: https://github.com/umbraco/Umbraco-CMS github.com: https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469 github.com: https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112 vulncheck.com: https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning
Credits
Eu Joe Chegne (Project Umbra) Damien Wong (Project Umbra) AndyButland