CVE-2026-117553
Received
Received - Intake
Authentication Bypass in Umbraco CMS via OAuth Redirect URI Poisoning
Vulnerability report for CVE-2026-117553, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-10-27
Last updated on: 2026-10-27
Assigner: VulnCheck
Description
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.
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| umbraco | Umbraco-CMS | 0 |
| umbraco | Umbraco-CMS | 18.0.0 |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-601 | The web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect. |
