CVE-2026-4634: A flaw was found in Keycloak

This month

HIGH 7.5REMOTEWATCHLISTDOWNGRADE

CVE-2026-4634 is a high-severity flaw (CVSS 7.5) affecting build of keycloak. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token endpoint. This leads to high resource consumption and prolonged processing times, ultimately resulting in a Denial of Service (DoS) for the Keycloak server.

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 50%)
CISA exploited list	No
Weakness	CWE-1050
Published	2026-04-02
Last modified	2026-10-26

Publisher (CNA): Red Hat, Inc. · Vendor: redhat

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-02 13:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

redhat build of keycloak DOWNGRADE

Affected: all versions · 26.2 · 26.2.15 · 26.4 · 26.4.11

Fixed in: no fixed release known

Safe to downgrade to: a release before 26.2

1. Check installed version

apt-cache policy build-of-keycloak || rpm -q build-of-keycloak || build-of-keycloak --version

2. No fixed release: DOWNGRADE to a release before 26.2 (Debian / Ubuntu)

apt-cache madison build-of-keycloak sudo apt install build-of-keycloak=<VERSION_BEFORE_26.2> sudo apt-mark hold build-of-keycloak

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list build-of-keycloak sudo dnf downgrade build-of-keycloak-<VERSION_BEFORE_26.2> sudo dnf versionlock add build-of-keycloak

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-4634?

build of keycloak: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-4634 being exploited?

CVE-2026-4634 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-4634 affect?

CVE-2026-4634 affects build of keycloak. Severity is high (CVSS 7.5). A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token endpoint. This leads to high re

How urgent is CVE-2026-4634?

Priority 49/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Keycloak vulnerabilities

Related CVEs

CVE-2026-4636 HIGH 8.1 DOWNGRADE A flaw was found in Keycloak
CVE-2026-4282 HIGH 7.4 DOWNGRADE A flaw was found in Keycloak
CVE-2026-3872 HIGH 7.3 DOWNGRADE A flaw was found in Keycloak
CVE-2026-37980 MEDIUM 6.9 MITIGATE A flaw was found in Keycloak, specifically in the organization selection login page
CVE-2026-4325 MEDIUM 5.3 DOWNGRADE A flaw was found in Keycloak

References

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