CVE-2026-117553
CVE-2026-117553 · Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning
This page contains facts from public vulnerability sources. Check the original advisory before updating.
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 7.7 · High · Fix available
- Published
- Updated
Affected products and versions
umbraco-cms
- Versions
- ≥ 0, < 17.7.2: Affected (semver)
- ≥ 18.0.0, < 18.2.2: Affected (semver)
Update to 17.7.2; Update to 18.2.2
Original sources
- https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6
- https://github.com/umbraco/Umbraco-CMS
- https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469
- https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112
- https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning
- https://nvd.nist.gov/vuln/detail/CVE-2026-117553