High severity7.5NVD Advisory· Published Oct 27, 2026· Updated Oct 27, 2026
CVE-2026-117553
CVE-2026-117553
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.
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Affected products
1- Range: <17.7.2 and <18.2.2
Patches
Vulnerability mechanics
References
4- github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.csnvd
- github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6nvd
- github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469nvd
- www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoningnvd
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