CVE-2026-117553
Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning
- State
- Published
- Severity
- 7.7 High
- Published
- Oct 27, 2026
- Updated
- Oct 27, 2026
- Reserved
- Oct 27, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 7.7 High | 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 | VulnCheck |
| 3.1 | 7.5 High | CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H | VulnCheck |
Weaknesses
- CWE-601 URL Redirection to Untrusted Site ('Open Redirect')
Affected Products
| Product | Versions |
|---|---|
Umbraco-CMSumbraco |
|
References
- Patch Commitpatch
- https://github.com/umbraco/Umbraco-CMSproduct
- GitHub Security Advisory (GHSA-rpv9-qp4c-g469)vendor-advisory
- https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112technical-description
- VulnCheck Advisory: Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoningthird-party-advisory
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