Medium [CVE-2026-21723] Denial of Service via uncontrolled memory usage in alertmanager templates
This medium-severity Red Hat Linux advisory covers CVE-2026-21723 affecting Multicluster Global Hub, Red Hat Advanced Cluster Management for Kubernetes 2, Red Hat Ceph Storage 5.
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Summary
The alertmanager templates test endpoint (/api/alertmanager/grafana/config/api/v1/templates/test) can execute templates with no memory limits. Mass-executing templates in a short period causes OOM and crashes the Grafana service.
The endpoint requires very low privileges and is exploitable with anonymous access enabled. A flaw was found in Grafana.
This can lead to an Out-Of-Memory (OOM) error, causing the Grafana service to crash and resulting in a Denial of Service (DoS). This Moderate flaw in Grafana allows a remote attacker to trigger a Denial of Service by repeatedly executing alertmanager templates.
While requiring low privileges, or anonymous access if enabled, the high attack complexity limits the immediate threat, as it relies on exhausting memory through mass template execution. Red Hat severity: Moderate — CVSS 5.3 (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H).
Weakness: CWE-770. Affected Red Hat products: Multicluster Global Hub; Red Hat Advanced Cluster Management for Kubernetes 2; Red Hat Ceph Storage 5; Red Hat Ceph Storage 6; Red Hat Ceph Storage 7; Red Hat Ceph Storage 8; Red Hat Ceph Storage 9; Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9.
Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Red Hat package: grafana.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 16 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 16 days ago·verify at source
Mitigation checklist
- If not required, disable anonymous access to prevent unauthenticated exploitation of the Alertmanager templates test endpoint. Refer to Grafana’s official documentation for configuration details. To protect against low-privileged authenticated users triggering this flaw, configure a reverse proxy or WAF to block or strictly rate-limit traffic to /api/alertmanager/grafana/config/api/v1/templates/test.
Official advisory · high-confidence parse· fetched 16 days ago·verify at source
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