# CVE-2020-27838: Keycloak discloses information without authentication

> Unauthenticated attackers can retrieve sensitive client secrets from public clients, potentially compromising confidentiality if clients later become confidential.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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:** Yes
- **Published:** 8 Mar 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-pcv5-m2wh-66j3

## What is CVE-2020-27838?

CVE-2020-27838 is a medium-severity vulnerability in Redhat Keycloak, published on 8 Mar 2021. 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 keycloak in versions prior to 13.0.0. The client registration endpoint allows fetching information about PUBLIC clients (like client secret) without authentication which could be an issue if the same PUBLIC client changed to CONFIDENTIAL later. The highest threat from this vulnerability is to data confidentiality.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2020-27838?

2 open source packages ship an affected version, including org.keycloak:keycloak-core. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `org.keycloak:keycloak-core` | Maven | All versions | 13.0.0 |
| `org.keycloak:keycloak-core` | Maven | All versions | 13.0.0 |

Products: Redhat Keycloak, Redhat Single Sign-On.

## How do I fix CVE-2020-27838?

Upgrade org.keycloak:keycloak-core to 13.0.0 or later.

## Is CVE-2020-27838 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2020-27838 exists.

Public exploit code:

- CVE-2020-27838 - KeyCloak - Information Exposure  (github_poc): https://github.com/Cappricio-Securities/CVE-2020-27838
- KeyCloak - Information Exposure (nuclei): http/cves/2020/CVE-2020-27838.yaml

## Other vulnerabilities in Redhat Keycloak

- [CVE-2022-4361](https://insights.sbomify.com/CVE-2022-4361/): Keycloak vulnerable to cross-site scripting when validating URI-schemes on SAML and OIDC (critical 10.0)
- [CVE-2022-1245](https://insights.sbomify.com/CVE-2022-1245/): Keycloak vulnerable to privilege escalation on Token Exchange feature (critical 9.8)
- [CVE-2021-20195](https://insights.sbomify.com/CVE-2021-20195/): keycloak Self Stored Cross-site Scripting vulnerability (critical 9.6)
- [CVE-2019-14910](https://insights.sbomify.com/CVE-2019-14910/): Keycloak Authentication Error (critical 9.3)
- [CVE-2019-14909](https://insights.sbomify.com/CVE-2019-14909/): Keycloak Authentication Error (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-27838 and fix it if it is affected.

What it is: CVE-2020-27838 is a medium-severity vulnerability in Redhat Keycloak, published on 8 Mar 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2020-27838 exists.

Affected packages and fixed versions:
- org.keycloak:keycloak-core (Maven): affected all versions; fixed in 13.0.0
- org.keycloak:keycloak-core (Maven): affected all versions; fixed in 13.0.0

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-2020-27838/ (Markdown: https://insights.sbomify.com/CVE-2020-27838/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-27838
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27838
- OSV: https://osv.dev/vulnerability/CVE-2020-27838

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-27838/
Summaries are generated and may contain mistakes; the official description above is the record.