What’s Vulnerable › Vulnerabilities

CVE-2026-16100: Keycloak-services: keycloak-services: unbounded metric cardinality in user event metrics via request-controlled error text

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-05 · updated 2026-08-31
• Weakness: CWE-770

Description

A flaw was found in the user-event metrics recording of Keycloak. When metrics are enabled, the system records raw error messages from failed account operations as Prometheus metric labels. Because these error messages can include user-supplied input like nonexistent client IDs, an authenticated user can create a massive number of unique metric entries, eventually exhausting system memory and causing the service to crash or become unavailable.

Affected products

• Red Hat build of Keycloak 26.4: from 26.6 before 26.6.5 — fixed in 26.6.5

How to fix

Upgrade to a fixed version: Red Hat build of Keycloak 26.4 26.6.5. Check the vendor advisory for mitigations.

References

• https://access.redhat.com/errata/RHSA-2026:50848
• https://access.redhat.com/errata/RHSA-2026:50849
• https://access.redhat.com/security/cve/CVE-2026-16100
• https://bugzilla.redhat.com/show_bug.cgi?id=2501730

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