CVE-2026-11800: A flaw was found in Keycloak

Routine

HIGH 8.1WATCHLISTUPGRADE

CVE-2026-11800 is a high-severity flaw (CVSS 8.1) 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. This JWT algorithm confusion vulnerability in the JWT Authorization Grant flow allows an attacker with valid client credentials to bypass signature verification. By forging an assertion, the attacker can create unauthorized access tokens. This enables the attacker to impersonate any federated user linked to the affected Identity Provider, leading to unauthorized access and potential privilege escalation.

Why this priority

High severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 77%)
CISA exploited list	No
Weakness	CWE-347
Published	2026-06-25
Last modified	2026-10-25

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

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-25 22:17 UTCPublished CVE record published
2026-10-25 22:10 UTCUpdated Record last modified

redhat build of keycloak UPGRADE

Affected: >= 26.6 and < 26.6.4

Fixed in: 26.6.4

Safe to downgrade to: a release before 26.6

1. Check installed version

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

2. UPGRADE to 26.6.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade build-of-keycloak

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade build-of-keycloak

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 26.6 (Debian / Ubuntu)

apt-cache madison build-of-keycloak sudo apt install build-of-keycloak=<VERSION_BEFORE_26.6> sudo apt-mark hold build-of-keycloak

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list build-of-keycloak sudo dnf downgrade build-of-keycloak-<VERSION_BEFORE_26.6> 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-2026-11800?

build of keycloak: upgrade to 26.6.4. Exact commands for each OS are on this page.

Is CVE-2026-11800 being exploited?

CVE-2026-11800 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-2026-11800 affect?

CVE-2026-11800 affects build of keycloak. Severity is high (CVSS 8.1). A flaw was found in Keycloak. This JWT algorithm confusion vulnerability in the JWT Authorization Grant flow allows an attacker with valid client credentials to bypass signature verification. By forging an assertion, the attacker can create

How urgent is CVE-2026-11800?

Priority 39/100. High severity; On your watchlist

Software pages

Keycloak vulnerabilities

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References

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