---
id: "CVE-2026-11800"
kind: "vulnerability"
aliases: ["CVE-2026-11800", "GHSA-j97h-3f8r-mrjr"]
title: "Keycloak has authentication bypass via jwt algorithm confusion"
severity: "high"
cvss: 8.1
epss: 0.003
exploited: false
status: "open"
category: "package"
products: [{"name": "org.keycloak:keycloak-services", "fixed": ["26.6.4"], "affected": "< 26.6.4", "ecosystem": "maven"}, {"name": "redhat build of keycloak", "fixed": ["26.6.4"], "affected": ">= 26.6, < 26.6.4", "ecosystem": "vendor"}]
ecosystems: ["maven", "vendor"]
tags: ["cwe-347", "identity", "java", "keycloak", "package", "self-hosted", "sso"]
not_affected_if: ["jwt-grant-unused", "keycloak-26.6.4-or-later", "managed-hosting"]
published_at: "2026-06-25T22:17:00+00:00"
first_seen_at: "2026-11-03T17:26:38+00:00"
updated_at: "2026-11-03T17:52:24+00:00"
sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-j97h-3f8r-mrjr", "first_seen_at": "2026-11-03T17:26:38+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-11800", "first_seen_at": "2026-11-03T17:52:24+00:00"}]
---

# Keycloak has authentication bypass via jwt algorithm confusion

Keycloak's JWT Authorization Grant flow accepts forged assertions because signature verification can be bypassed through algorithm confusion. An attacker with valid client credentials can mint access tokens and impersonate federated users linked to an identity provider.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- maven:org.keycloak:keycloak-services affected < 26.6.4 fixed 26.6.4
- vendor:redhat build of keycloak affected >= 26.6, < 26.6.4 fixed 26.6.4

## How to check

- Check the Keycloak version with the server's version output or the `keycloak-services` artifact version in your build; affected versions are below `26.6.4`.
- Look for use of the JWT Authorization Grant flow (client authentication with signed assertions) in your realm configuration.

## Fix

- Keycloak `keycloak-services`: upgrade to `26.6.4`

## Timeline

- 2026-11-03T17:26:38+00:00 ghsa https://github.com/advisories/GHSA-j97h-3f8r-mrjr
- 2026-11-03T17:52:24+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-11800

## Documents

- [advisory] Maintainer's advisory: api.github.com https://api.github.com/repos/keycloak/keycloak/security-advisories/GHSA-j97h-3f8r-mrjr
- [advisory] Maintainer's advisory: github.com https://github.com/keycloak/keycloak/security/advisories/GHSA-j97h-3f8r-mrjr
- [advisory] Vendor advisory: security.access.redhat.com https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-11800.json
- [advisory] Third-party advisory: access.redhat.com https://access.redhat.com/errata/RHSA-2026:30083
- [advisory] Third-party advisory: access.redhat.com https://access.redhat.com/errata/RHSA-2026:30084
- [advisory] Vendor advisory: access.redhat.com https://access.redhat.com/security/cve/CVE-2026-11800
- [advisory] Vendor advisory: bugzilla.redhat.com https://bugzilla.redhat.com/show_bug.cgi?id=2487006
- [fix] Patch: github.com https://github.com/keycloak/keycloak/commit/6d61885f20ac59a2ff8b823fc9ed1f1ef1019951
- [fix] Patch: github.com https://github.com/keycloak/keycloak/commit/d343c7373dcc7bfeb9dc14de2309836299c81837
- [fix] Release: github.com https://github.com/keycloak/keycloak/releases/tag/26.6.4
- [fix] Patch: github.com https://github.com/keycloak/keycloak/pull/50374

## From the sources

### Description
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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_