Red Hat Keycloak/Single Sign-On Login Theme Rendering improper authorization

Summaryinfo

A vulnerability, which was classified as problematic, has been found in Red Hat Keycloak and Single Sign-On. Impacted is an unknown function of the component Login Theme Rendering Component. This manipulation causes improper authorization. This vulnerability is tracked as CVE-2026-107889. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in Red Hat Keycloak and Single Sign-On (affected version unknown). It has been declared as problematic. Affected by this vulnerability is an unknown functionality of the component Login Theme Rendering Component. The manipulation with an unknown input leads to a improper authorization vulnerability. The CWE definition for the vulnerability is CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

A flaw was found in the login theme rendering component of Keycloak. The issue occurs because the security filter responsible for cleaning user input can be bypassed, allowing a realm administrator to store malicious scripts in display fields. This could result in unauthorized JavaScript execution in the browsers of users visiting the login page, potentially leading to data exposure or session interference.

The advisory is shared at access.redhat.com. This vulnerability is known as CVE-2026-107889 since 10/09/2026. The exploitation appears to be easy. The attack can be launched remotely. Additional levels of successful authentication are required for exploitation. It demands that the victim is doing some kind of user interaction. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 10/10/2026). MITRE ATT&CK project uses the attack technique T1548.002 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the databases at EUVD (EUVD-2026-95478) and CERT Bund (WID-SEC-2026-3849). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

• Open Source Keycloak

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Vendor

• Red Hat

Name

• Keycloak
• Single Sign-On

License

• open-source

Website

• Vendor: https://www.redhat.com/

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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