Quick answers
- Is CVE-2026-18211 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-18211 being exploited in the wild.
- How severe is CVE-2026-18211?
- Medium severity, with a CVSS score of 4.2, published 31 July 2026.
- Which products and versions are affected?
- Red Hat build of Keycloak All versions using keycloak-services package.
- Is there a fix for CVE-2026-18211?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-18211 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-18211?
- Check whether you run Red Hat build of Keycloak at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A vulnerability exists in the 'secure-client-uris' client policy executor within Keycloak's core services (keycloak-services). The executor fails to properly validate the host component of redirect URIs when 'allow-http-on-localhost' is enabled, instead performing a simple string prefix check for 'http://localhost' or 'http://127.0.0.1'. An attacker can exploit this by registering a client via Dynamic Client Registration using a malicious URI that starts with the allowed prefix but resolves to an attacker-controlled domain (e.g., 'http://localhost.attacker.com'). When a victim authenticates, the authorization code is transmitted over cleartext HTTP to the attacker's server. This is classified as improper input validation (CWE-20).
Affected products
- Red Hat Red Hat Build of Keycloak All versions using keycloak-services package
Timeline
- 2026-07-29: disclosed: Reported via Red Hat Bugzilla
- 2026-07-31: advisory: NVD published the CVE record