CVE-2023-6563 is a vulnerability identified in Red Hat Single Sign-On (RH-SSO) version 7.6 running on Red Hat Enterprise Linux 7. The root cause is an allocation of resources without limits or throttling within the Keycloak component that RH-SSO is based on. Specifically, when an environment contains an extremely large number of offline tokens—such as more than 500,000 users each with at least two saved sessions—the administrative User Interface's 'consents' tab attempts to load all offline client sessions without any constraints. An attacker who can create two or more user sessions and access this tab triggers the loading of a massive volume of offline client session data. This results in excessive consumption of memory and CPU resources, which can overwhelm the system and cause it to crash, leading to a denial-of-service (DoS) condition. The vulnerability requires the attacker to have limited privileges (PR:L) but does not require user interaction beyond the attacker’s own actions (UI:N). The CVSS v3.1 score is 7.7 (high), reflecting the network attack vector, low attack complexity, and the impact on availability with no impact on confidentiality or integrity. No known exploits have been reported in the wild as of the publication date. The vulnerability is particularly relevant for large-scale deployments of RH-SSO where offline token counts are very high, such as large enterprises or service providers. The lack of resource throttling in the admin UI’s session loading mechanism is the key technical flaw. This vulnerability highlights the risks of unbounded resource consumption in identity and access management systems, which can be exploited to cause service outages.

For European organizations, the primary impact of CVE-2023-6563 is the potential for denial-of-service attacks against critical identity management infrastructure. RH-SSO is often used to provide centralized authentication and authorization services for enterprise applications, cloud platforms, and government services. A successful exploitation could lead to system crashes, causing authentication outages and disrupting access to multiple dependent services. This can affect business continuity, user productivity, and potentially compliance with regulations requiring high availability of identity services. Organizations with very large user bases or those managing millions of offline tokens are at greatest risk. The vulnerability does not expose sensitive data or allow privilege escalation but severely impacts availability, which can have cascading effects on operational security and service delivery. Given the reliance on RH-SSO in sectors such as finance, telecommunications, and public administration in Europe, the disruption could have significant operational and reputational consequences. Additionally, the attack requires only limited privileges, increasing the risk from insider threats or compromised low-privilege accounts. The absence of known exploits in the wild suggests a window of opportunity for proactive mitigation before active exploitation occurs.

To mitigate CVE-2023-6563, European organizations should implement the following specific measures: 1) Apply any available patches or updates from Red Hat promptly once released, as these will likely address the resource allocation flaw. 2) Limit the number of offline tokens per user and overall offline token counts to reduce the volume of data loaded by the admin UI. This can be done by enforcing token expiration policies and cleaning up stale sessions regularly. 3) Restrict access to the admin User Interface, especially the 'consents' tab, to trusted administrators only, using network segmentation, multi-factor authentication, and strict role-based access controls. 4) Monitor memory and CPU usage on RH-SSO servers closely to detect abnormal spikes that could indicate exploitation attempts. 5) Consider implementing rate limiting or throttling mechanisms at the application or infrastructure level to prevent excessive resource consumption triggered by UI actions. 6) Conduct regular audits of user sessions and offline tokens to identify and remediate unusually large session counts. 7) Engage with Red Hat support and security advisories to stay informed about updates and best practices. These targeted mitigations go beyond generic advice by focusing on token management, access control, and resource monitoring specific to the vulnerability’s exploitation vector.