CVE-2023-6563VulnerabilityPublished 14 Dec 2023Updated 11 Nov 2025

CVE-2023-6563: Red Hat Single Sign-On 7.6 for RHEL 7 · Unthrottled Resource Allocation

Affects Red Hat Single Sign-On 7.6 for RHEL 7Source CVE Database V5

Not known to be exploited · CVSS 7.7 High.

Data as of 26 Oct 2026, 07:57 UTC

CVSS 3.1 base score

7.7High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 1.2% chance of exploitation in 30 days – higher than 68% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 14 Dec 2023
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

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.

Description

An unconstrained memory consumption vulnerability was discovered in Keycloak. It can be triggered in environments which have millions of offline tokens (> 500,000 users with each having at least 2 saved sessions). If an attacker creates two or more user sessions and then open the "consents" tab of the admin User Interface, the UI attempts to load a huge number of offline client sessions leading to excessive memory and CPU consumption which could potentially crash the entire system.

Impact

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.

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 11 Nov 2025, 16:07 UTC

Technical details

References

Community reviews

Related threats