# CVE-2026-18206: Keycloak-services: keycloak-services: client policy source-host wildcard domain matching bypass

> Attackers can bypass client registration restrictions by exploiting improper wildcard domain validation in Keycloak, allowing unauthorized client modifications.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 31 Jul 2026
- **Updated:** 31 Aug 2026
- **Also known as:** GHSA-2w88-g477-cxmj

## What is CVE-2026-18206?

CVE-2026-18206 is a low-severity vulnerability in Redhat Build of Keycloak, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw was found in the keycloak-services component of Keycloak, which provides identity and access management services. The issue occurs when a realm administrator uses a wildcard domain (like *.example.com) to restrict which hosts can register or update clients. Due to improper validation, the system accepts any hostname that ends with the specified domain suffix, even if it is not a legitimate subdomain. An attacker who can control the reverse DNS of their connection can bypass these host-based restrictions, potentially allowing unauthorized client modifications.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-18206?

It affects 1 product.


Products: Redhat Build of Keycloak.

## How do I fix CVE-2026-18206?

No fix has been published for CVE-2026-18206 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18206 being exploited?

There is no known exploitation of CVE-2026-18206 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-2026-18206 and fix it if it is affected.

What it is: CVE-2026-18206 is a low-severity vulnerability in Redhat Build of Keycloak, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-18206 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-2026-18206/ (Markdown: https://insights.sbomify.com/CVE-2026-18206/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18206
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18206
- OSV: https://osv.dev/vulnerability/CVE-2026-18206

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18206/
Summaries are generated and may contain mistakes; the official description above is the record.