CVE-2026-88770 in Keycloak
Summary
by MITRE • 09/10/2026
A flaw was found in the Device Authorization Grant flow of Keycloak, an identity and access management solution. The issue occurs because the token redemption process fails to check if a user account is currently locked due to brute-force protection. If an attacker has an active session for a locked account, they can complete the device login process and receive new security tokens. This allows the attacker to maintain access to the account even when it should be temporarily disabled to prevent unauthorized entry.
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Analysis
by VulDB Data Team • 09/10/2026
The vulnerability identified in Keycloak represents a critical bypass of brute-force protection mechanisms within the Device Authorization Grant flow, an OAuth 2.0 extension designed for devices with limited input capabilities such as smart TVs or IoT appliances. This flaw stems from a logical inconsistency in how the token redemption endpoint validates user account status against security policies. Specifically, when a client application requests new access tokens using a device code and user verification code, Keycloak fails to verify whether the associated user account has been temporarily locked due to excessive failed login attempts. In standard authentication flows, such locks are enforced by checking the account's lockout state before issuing credentials or session updates. However, in this specific grant type, the system proceeds with token generation without performing this crucial check, effectively treating a locked account as if it were active and eligible for credential issuance.
From an operational perspective, this oversight allows attackers to maintain persistent access to compromised accounts even after security controls have been triggered to mitigate ongoing brute-force attacks. If an attacker has previously obtained valid session cookies or tokens for a target user before the lockout was initiated, they can leverage these existing credentials through the device authorization flow to refresh their authentication state. This capability negates the primary purpose of account lockouts, which is to disrupt automated attack campaigns by forcing attackers to wait out a cooldown period or reset their progress. Consequently, an adversary who has already established a foothold within the identity provider's session layer can bypass temporary restrictions and continue performing authenticated actions against protected resources without triggering additional alerts associated with new login attempts.
This vulnerability aligns closely with CWE-287 Improper Authentication, as it involves a failure to correctly enforce authentication policies during specific operational contexts. Furthermore, it relates to CWE-613 Insufficient Session Expiration because the ability to refresh tokens indefinitely extends the lifespan of potentially compromised sessions beyond intended limits. In terms of MITRE ATT&CK mapping, this behavior facilitates Account Manipulation and Credential Access techniques, allowing attackers to sustain their presence within a network environment by circumventing defensive measures designed to detect or halt unauthorized access attempts. The lack of state validation during token redemption creates an opportunity for privilege persistence that is difficult to detect through standard login monitoring logs alone.
To mitigate this risk, administrators should ensure they are running the latest patched version of Keycloak where this logic error has been corrected by enforcing account lockout checks across all authentication flows, including device authorization grants. Additionally, organizations employing multi-factor authentication can reduce reliance on brute-force protection mechanisms for certain high-value accounts, although this does not fully address the underlying flaw in session management. Security teams should also monitor for unusual patterns of token refreshes from non-standard client applications or devices that do not typically utilize the Device Authorization Grant flow, as such activity may indicate exploitation attempts against vulnerable instances before patches are applied.