# CVE-2026-18211: Keycloak secure-client-uris policy bypass via improper host validation

Source: https://junglewise.ai/threats/cve-2026-18211-keycloak-secure-client-uris-policy-bypass-via-improper-host  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-31. Updated: 2026-07-31  
License: CC BY 4.0 with a link back

CVE-2026-18211 · Severity: medium · CVSS 4.2 · Published 2026-07-31

Keycloak, an open-source identity and access management solution, contains a security flaw in how it validates web addresses for client applications. The system is designed to ensure that sensitive login data is only sent over secure, encrypted connections, but a bug allows attackers to bypass this check by using specially crafted domain names that mimic trusted local addresses. If exploited, an attacker could intercept a user's authentication codes over an unencrypted connection, potentially leading to unauthorized account access.

Technologies: [Red Hat build of Keycloak](https://junglewise.ai/threats/technologies/red-hat-keycloak). Vendors: [Red Hat](https://junglewise.ai/threats/vendors/red-hat).

## 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

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/jbossnetwork/restricted/listSoftware.html](https://access.redhat.com/jbossnetwork/restricted/listSoftware.html)
- [https://access.redhat.com/security/cve/CVE-2026-18211](https://access.redhat.com/security/cve/CVE-2026-18211)
- [https://bugzilla.redhat.com/show_bug.cgi?id=2508306](https://bugzilla.redhat.com/show_bug.cgi?id=2508306)

## Related threats

- [Keycloak server arbitrary code execution in client authorization](https://junglewise.ai/threats/cve-2026-120984-a-flaw-was-found-in-the-keycloak-server-s-client-management)
- [Red Hat Build of Keycloak OIDC logout session fixation](https://junglewise.ai/threats/cve-2026-107124-a-flaw-was-found-in-the-oidc-logout-endpoint-of-the-keycloak)
- [Keycloak theme resource disk exhaustion](https://junglewise.ai/threats/cve-2026-110932-a-flaw-was-found-in-the-theme-resource-endpoint-of-keycloak-an)
- [Keycloak secure-redirect-uris-enforcer open redirect via DNS resolution](https://junglewise.ai/threats/cve-2026-118425-a-flaw-was-found-in-the-secure-redirect-uris-enforcer-client)
- [Keycloak OIDC Dynamic Client Registration offline token revocation bypass](https://junglewise.ai/threats/cve-2026-107623-a-flaw-was-found-in-the-oidc-dynamic-client-registration-dcr)