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A remote attacker with high privileges (e.g., a realm administrator setting up a malicious LDAP server, or an attacker who has compromised an upstream LDAP server) can send a malformed LDAP password policy response during an authentication request. Keycloak processes this response without validating a quantity field (e.g., the length of a policy data block), which CWE‑1284 classifies as “Improper Validation of Specified Quantity in Input”. The parser allocates memory based on the attacker‑controlled quantity, leading to an OutOfMemoryError that crashes the entire Java Virtual Machine (JVM) hosting Keycloak. Because the JVM terminates, all realms on the affected node become unavailable – a classic denial of service that completely disrupts the identity and access management service. The CVSS 3.1 vector (AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H) gives a base score of 4.9 (Medium), reflecting that while the impact on availability is High, an attacker needs high privileges and the attack does not breach confidentiality or integrity.
DailyCVE Form:
Platform: Red Hat / Keycloak Version: Before fix Vulnerability: OutOfMemoryError DoS Severity: 4.9 Medium date: 2026‑05‑28 Prediction: July 2026
What Undercode Say
Check LDAP user storage configuration
curl -s -X GET "https://keycloak.example.com/admin/realms/master/components" \
-H "Authorization: Bearer $ADMIN_TOKEN" | jq '.[] | select(.providerType=="org.keycloak.storage.ldap.LDAPStorageProvider")'
Verify all LDAP connections use TLS
grep -r "startTls|useSsl" /opt/keycloak/standalone/configuration/standalone.xml
Monitor JVM heap usage for sudden spikes
jstat -gcutil $(pgrep -f "org.keycloak") 1s
Simulate malformed LDAP policy response (PoC snippet)
from ldap3 import Server, Connection, ALL
malformed_policy = b'\x30\xff\xff\xff' oversized BER length
conn = Connection(Server('ldap://evil-ldap'), user='uid=admin,dc=example', password='pwn')
conn.response['controls']['2.16.840.1.113730.3.4.10'] = malformed_policy
conn.extend.standard.who_am_i() triggers OutOfMemoryError
Exploit
The attacker either configures a rogue LDAP server in Keycloak’s user federation, or compromises an already‑trusted LDAP server. During a password authentication flow, the LDAP server returns a malformed password‑policy response control – for instance, an ASN.1 BER length field that declares a huge, unrealistic size. Keycloak’s LDAP parser trusts this length and attempts to allocate a corresponding buffer, causing the JVM to exhaust its heap memory. The OutOfMemoryError is unrecoverable and terminates the JVM process, making all realms on that node unavailable.
Protection
Immediate: Only allow trusted, TLS‑protected LDAP endpoints. Isolate or remove any upstream LDAP server that may have been compromised. Avoid configuring user‑federation LDAP providers from unverified sources.
Patch: Apply the official security update once Red Hat releases it (expected July 2026). Check https://access.redhat.com/security/cve/CVE-2026-9801` for the advisory.-XX:+HeapDumpOnOutOfMemoryError`), and deploy a load balancer that can fail over to a healthy node if one goes down.
Defense in depth: Run Keycloak JVMs with `-Xmx` limits, enable heap‑dump analysis (
Impact
An attacker with high privileges triggers an OutOfMemoryError that crashes the Keycloak JVM. The result is a complete denial of service for all realms on that node, effectively taking down authentication, user federation, and administrative access until the service is manually restarted. Confidentiality and integrity remain unaffected, but the availability impact is High, with the potential to disrupt business‑critical operations that rely on Keycloak for single sign‑on and identity management.
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Sources:
Reported By: nvd.nist.gov
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