# CVE-2026-18211: Keycloak-services: keycloak-services: secure-client-uris policy bypass via localhost-prefixed domains

> Attackers can bypass secure-client-uris policies using crafted domains to intercept authentication codes over unencrypted connections in Keycloak.

- **Severity:** Medium 4.2 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 31 Jul 2026
- **Updated:** 31 Aug 2026
- **Also known as:** GHSA-6j79-4gfx-fm6f

## What is CVE-2026-18211?

CVE-2026-18211 is a medium-severity vulnerability in Redhat Build of Keycloak, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

A flaw was found in the secure-client-uris client policy executor within Keycloak core services. This component is responsible for enforcing security requirements on client configurations, such as requiring encrypted connections for redirect URIs. Due to an improper check that only looks at the start of a web address rather than properly verifying the host, an attacker can bypass these security restrictions by using a specially crafted domain name. This could allow an attacker to intercept sensitive authentication codes over unencrypted connections.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-18211?

It affects 1 product.


Products: Redhat Build of Keycloak.

## How do I fix CVE-2026-18211?

No fix has been published for CVE-2026-18211 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18211 being exploited?

There is no known exploitation of CVE-2026-18211 in the wild and no public exploit code.

## Other vulnerabilities in Redhat Build of Keycloak

- [CVE-2026-15572](https://insights.sbomify.com/CVE-2026-15572/): Keycloak-services: keycloak-services: dcr protocol mapper type-swap policy bypass allows privilege escalation (high 8.8)
- [CVE-2026-3047](https://insights.sbomify.com/CVE-2026-3047/): Keycloak SAML Broken has Authentication Bypass by Primary Weakness (high 8.8)
- [CVE-2026-15573](https://insights.sbomify.com/CVE-2026-15573/): Keycloak-services: keycloak-services: authorization bypass via unnormalized uri matching in pathmatcher (high 8.1)
- [CVE-2026-16102](https://insights.sbomify.com/CVE-2026-16102/): Keycloak-services: keycloak-services: default dcr policy allows role forgery via user property mappers (high 8.1)
- [CVE-2026-1609](https://insights.sbomify.com/CVE-2026-1609/): Org.keycloak/keycloak-quarkus-server: keycloak: unauthorized access via jwt authorization grant with disabled users (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18211 and fix it if it is affected.

What it is: CVE-2026-18211 is a medium-severity vulnerability in Redhat Build of Keycloak, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-18211 in the wild and no public exploit code.

Affected product: Redhat Build of Keycloak. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-18211/ (Markdown: https://insights.sbomify.com/CVE-2026-18211/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18211
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18211
- OSV: https://osv.dev/vulnerability/CVE-2026-18211

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18211/
Summaries are generated and may contain mistakes; the official description above is the record.