CVE-2026-117553 Umbraco CMS - Authentication Bypass

Umbraco CMS < 17.7.2 and < 18.2.2 contains an authentication bypass caused by Host header poisoning in OAuth redirect URI registration, letting unauthenticated attackers hijack back-office sessions and execute code via Razor templates, exploit requires sending signed-in users authorization links.

CVSS base score 7.5 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.50% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Authentication Bypass
Impact
Remote Code Execution, Privilege Escalation
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Published
27 October 2026
Updated
29 October 2026
Weakness
CWE-601

Vendor fix

Upgrade to versions 17.7.2 or 18.2.2 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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