CVE-2026-9088: Keycloak Delegated Admin Bypass Information Disclosure Vulnerability

Technical summary

CVE-2026-9088 affects org.keycloak.services and stems from insufficient access control enforcement on the group members endpoint. The vulnerability allows a delegated administrator to bypass user profile permission checks designed to restrict visibility of certain user attributes. An attacker with group-read and user-read delegations can extract forbidden user data by directly querying the group members API, bypassing the profile-level authorization logic that should enforce attribute-level denial rules. The flaw is rooted in CWE-1220 (Improper Restriction of Rendered UI Layers or Frames), indicating a control bypass at the API layer.

Business impact

This vulnerability primarily affects organizations using Keycloak's role-based delegation model to separate administrative duties. If an administrator role is scoped to manage only certain groups or read user lists, a compromised or malicious delegated admin could extract personal information (phone numbers, email addresses, custom attributes) that the organization intentionally restricted from their role. The impact is information disclosure; no data modification or system availability impact occurs. Risk is highest in multi-tenant or federated identity scenarios where attribute privacy is a compliance or contractual requirement.

Affected systems

Keycloak deployments using delegated administrative roles with granular permission scoping are affected. The vulnerability applies to any instance where user profile attributes are configured with deny rules and delegated admins hold read permissions on groups or users. No specific version constraints were provided in the source data; verify the vendor advisory for affected Keycloak versions and patch availability.

Exploitability

Exploitation requires an existing admin account with delegated read access to groups and users—a non-trivial prerequisite that limits opportunistic attack. An attacker cannot exploit this remotely without valid credentials. Network access is required but automated; no user interaction or complex exploitation techniques are needed. The low CVSS score (2.7) reflects these constraints: high privilege requirement (PR:H), local scope impact, and read-only access (C:L, I:N, A:N).

Remediation

Apply the Keycloak patch addressing this authorization bypass when available from the vendor. Pending patch deployment, audit delegated administrative roles to confirm their scope aligns with organizational intent; remove unnecessary user-read or group-read permissions from roles that do not require them. Consider implementing additional API-level monitoring to detect unusual queries to the group members endpoint by delegated accounts.

Patch guidance

Check the Keycloak security advisories for a patched release addressing CVE-2026-9088. Apply patches to all Keycloak instances running vulnerable versions, prioritizing environments where delegated admin roles are in active use. Verify patch installation by confirming the group members endpoint enforces user profile permission rules and denies access to restricted attributes.

Detection guidance

Monitor Keycloak audit logs for repeated or bulk queries to the group members endpoint by delegated administrator accounts, particularly if followed by requests for user attributes marked as restricted. Log any access that returns user data contradicting the administrator's delegated permissions. Implement application-level instrumentation to flag unauthorized attribute disclosure attempts.

Why prioritize this

Although the CVSS score is low, this vulnerability warrants prompt patching because it undermines the administrative control model that many organizations rely on for compliance and data governance. The flaw is deterministic—if an admin has the necessary delegations, the exploit is trivial—and affects the integrity of access control assumptions. Organizations with strict attribute privacy requirements should prioritize remediation.

Risk score, explained

The CVSS 3.1 score of 2.7 reflects a flaw with high privilege requirement (PR:H), network accessibility (AV:N), low complexity attack (AC:L), unchanged scope (S:U), and limited confidentiality impact (C:L). No integrity or availability impact occurs. The score is appropriate for a delegated admin bypass with information disclosure only; however, the real-world risk depends on the sensitivity of restricted attributes and the trust assumptions for delegated roles in your deployment.

Frequently asked questions