CVE-2026-117553
Umbraco CMS before 17.7.2 and 18.2.2 contains an authentication bypass vulnerability that allows…
- Risk score
- 50/100
- CVSS
- 7.5 v3.1
- Published
- 27 Oct 2026
Open in the live forecast Today's forecast
What to know
- What it is
- 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 the…
- Affected
- See advisory
- Fix
- Upgrade the product to 17.7.2 or 18.2.2 (whichever matches your release line), or later.
- Exploitation
- No known exploitation
Why it is Yellow
- CVSS 7.5 high
- Remotely exploitable without logging in
References
- https://github.com/umbraco/Umbraco-CMS
- https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112
- https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6
- https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469
- https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning
Original 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.
Last activity 27 Oct 2026. Patch Forecast updates every hour.