CVE-2026-117553
High · 7.5CVSS
7.5
EPSS
0.5%
Published
Oct 27, 2026
CISA due date
—
The record
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.
Affected packages
| Ecosystem | Package | Introduced | Fixed |
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