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MEDIUM severity

CVE-2026-9704 — keycloak-server-spi-priva…

MEDIUMFix: keycloak/keycloak#49472

CVE-2026-9704 is a medium-severity (CVSS 6.8) CWE-1284 vulnerability in org.keycloak:keycloak-server-spi-private. A fix is available for org.keycloak:keycloak-server-spi-private — see the affected versions and patch details below.

Keycloak Vulnerable to Improper Validation of Specified Quantity in Input

Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Oct 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • A successful exploit gives an attacker total control of the affected component, not partial access.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-9704.

EPSS Exploitation Probability

via FIRST.org ↗
0.6%probability of exploitation in next 30 days
Lower Risk+0.27%
Lower risk than most CVEs46th percentile — riskier than 46% of all scored CVEsHighest risk
0.00%0.36%0.72%1.09%0.3%0.6%Jul 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-9704 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 384,534 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected
☕org.keycloak:keycloak-server-spi-private☕org.keycloak:keycloak-services

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.keycloak:keycloak-server-spi-privateall versions26.6.3org.keycloak:keycloak-server-spi-private:26.6.3
☕Mavenorg.keycloak:keycloak-servicesall versions26.6.3org.keycloak:keycloak-services:26.6.3

Affected Products

1 product · 1 configurations
Application
build of keycloakredhat
all

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.keycloak:keycloak-server-spi-private, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.keycloak:keycloak-server-spi-private to 26.6.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-9704 is resolved across your whole dependency graph.

  3. Workarounds

    Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This Moderate flaw in Keycloak allows an authenticated, low-privileged user to escalate privileges. By submitting an oversized `subject_token` JWT to the TokenEndpoint, the system defaults to client credentials, granting the attacker the client's service account permissions. This bypass occurs when the token exceeds a…

Workaround published by Red Hat
To prevent the silent dropping of oversized `subject_token` JWTs, configure Keycloak to enforce strict parameter validation. This involves setting the `fail-fast` parameter to `true` for the `TokenEndpoint` configuration, which will cause requests with oversized parameters to be rejected explicitly rather than silently processed with reduced privileges. Consult Keycloak documentation for the exact method to modify these settings. A restart of the Keycloak service may be necessary for the changes to apply.
Source: Red Hat security advisory for CVE-2026-9704 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat build of Keycloak 26.4rhbk/keycloak-operator-bundle:26.4.13-1RHSA-2026:30050
Red Hat build of Keycloak 26.4.13rhbk/keycloak-rhel9RHSA-2026:30049
Red Hat build of Keycloak 26.6rhbk/keycloak-operator-bundle:26.6.3-3RHSA-2026:25097
Red Hat build of Keycloak 26.6.3rhbk/keycloak-rhel9RHSA-2026:25098

Frequently Asked Questions

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.
O3 Security · Impact-Aware SCA

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CVE-2026-9704: keycloak-server-spi — Fixed in 26.6.3