CVE-2026-9704 Keycloak: keycloak: privilege escalation due to oversized subject_token jwt
Low-privilege users can escalate privileges by sending oversized JWTs that trigger a fallback to client credentials in Keycloak.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-9704?
CVE-2026-9704 is a medium-severity vulnerability in Redhat Build of Keycloak, published on 27 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
A flaw was found in Keycloak. An authenticated user with low privileges can exploit this vulnerability by sending an oversized subject_token JSON Web Token (JWT) to the TokenEndpoint. When the token exceeds a 4000-character limit, it is silently dropped, causing the system to fall back to client credentials. This allows the user to gain the permissions of the client's service account, leading to privilege escalation.
Weakness: CWE-1284
Which versions are affected by CVE-2026-9704?
4 open source packages ship an affected version, including org.keycloak:keycloak-server-spi-private and org.keycloak:keycloak-services. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
org.keycloak:keycloak-server-spi-private Maven | All versions | 26.6.3 |
org.keycloak:keycloak-server-spi-private Maven | All versions | 26.6.3 |
org.keycloak:keycloak-services Maven | All versions | 26.6.3 |
org.keycloak:keycloak-services Maven | All versions | 26.6.3 |
Products include Redhat Build of Keycloak.
How do I fix CVE-2026-9704?
Upgrade org.keycloak:keycloak-server-spi-private to 26.6.3 or later.
Is CVE-2026-9704 being exploited?
There is no known exploitation of CVE-2026-9704 in the wild and no public exploit code.
Other vulnerabilities in Redhat Build of Keycloak
- CVE-2026-15572 Keycloak-services: keycloak-services: dcr protocol mapper type-swap policy bypass allows privilege escalation
- CVE-2026-3047 Keycloak SAML Broken has Authentication Bypass by Primary Weakness
- CVE-2026-15573 Keycloak-services: keycloak-services: authorization bypass via unnormalized uri matching in pathmatcher
- CVE-2026-16102 Keycloak-services: keycloak-services: default dcr policy allows role forgery via user property mappers
- CVE-2026-1609 Org.keycloak/keycloak-quarkus-server: keycloak: unauthorized access via jwt authorization grant with disabled users
Sources
Also known as ECHO-1969-c688-a45c, GHSA-rr5q-3xwr-f323, MINI-fp25-7wqp-crch, MINI-gq94-v5qx-vxp4.