---
id: "GHSA-gqj5-2xp5-3qmp"
kind: "vulnerability"
aliases: ["GHSA-gqj5-2xp5-3qmp"]
title: "Duplicate Advisory: Authentication bypass via jwt algorithm confusion"
severity: "high"
cvss: 8.1
epss: null
exploited: false
status: "withdrawn"
category: "runtime"
products: [{"name": "org.keycloak:keycloak-services", "fixed": ["26.6.4"], "affected": "< 26.6.4", "ecosystem": "maven"}]
ecosystems: ["maven"]
tags: ["cwe-347", "identity-federation", "keycloak", "maven", "runtime", "self-hosted"]
not_affected_if: ["keycloak-26.6.4-or-later"]
published_at: "2026-06-26T00:32:05+00:00"
first_seen_at: "2026-11-03T17:26:38+00:00"
updated_at: "2026-11-03T17:28:09+00:00"
sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-gqj5-2xp5-3qmp", "first_seen_at": "2026-11-03T17:26:38+00:00"}]
---

# Duplicate Advisory: Authentication bypass via jwt algorithm confusion

Keycloak's JWT Authorization Grant flow accepts forged assertions because it skips signature verification through algorithm confusion. An attacker with valid client credentials can mint access tokens and impersonate any user linked to the affected 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

## How to check

- Check the Keycloak server version; affected releases are below `26.6.4`.
- Check whether the JWT Authorization Grant flow is in use: unknown from the sources.

## Fix

- Keycloak: move to `26.6.4`.

## Timeline

- 2026-11-03T17:26:38+00:00 ghsa https://github.com/advisories/GHSA-gqj5-2xp5-3qmp

## From the sources

### Duplicate Advisory
This advisory has been withdrawn because it is a duplicate of GHSA-j97h-3f8r-mrjr. This link is maintained to preserve external references.

### Original 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_