7.3 High

Keycloak vulnerable to cross-site scripting (xss) via case-insensitive uri validation bypass

CVE-2026-9086

Description A flaw was found in Keycloak. A remote attacker with administrative privileges, specifically those with manage-client permission or access to client registration endpoints, could bypass client Uniform Resource Identifier (URI) validation. This is achieved by registering a malicious client with a specially crafted redirect URI using a case-insensitive javascript: or data: scheme. This Cross-Site Scripting (XSS) vulnerability allows for arbitrary code execution in the Keycloak origin when a victim clicks the crafted link, such as in the logout flow or the Admin Console.

Proof-of-concept code is published

Public PoC

Public PoCSaku0512/CVE-2026-9086-poc1 stars

Signals come from Exploit-DB, Metasploit, Nuclei and published proof-of-concept repositories. Their absence means nothing was found, not that nothing exists.

Assessment

CVSS: 7.3 (v3.1)
Severity: High
EPSS: 0.00781% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Public PoC
Published: 29 October 2026
Last updated: 29 October 2026
Affected: maven · org.keycloak:keycloak-services
Weakness: CWE-79

CVSS vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N

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