Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning

Summary

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.

Remediation

1. Inventory every umbraco Umbraco-CMS deployment, including staging.
2. Upgrade umbraco Umbraco-CMS to the fixed version for your release line, listed under Affected versions.
3. Confirm the running version after the upgrade.

References

• Patchhttps://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6
• Advisoryhttps://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469
• Advisoryhttps://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning
• Referencehttps://github.com/umbraco/Umbraco-CMS
• Referencehttps://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112