Vulnerability 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.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/umbraco/Umbraco-CMS
- https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.M
- https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b
- 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-accoun
FAQ
What is CVE-2026-117553?
CVE-2026-117553 is a vulnerability with a CVSS score of 7.5 (HIGH). 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 hea...
How severe is CVE-2026-117553?
CVE-2026-117553 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-117553?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.