Live › vulnerability › CVE-2026-81938
Grafana Mimir's Alertmanager did not block tenant configurations that point HTTP header or basic auth username fields at local files. A tenant who can write an Alertmanager configuration can send those file contents to a server they control, exposing credentials and configuration from the Alertmanager host.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-11-02 19:24 UTC. All times on this page are UTC.
Teams running Grafana Mimir or Grafana Enterprise Metrics with multiple tenants who can upload their own Alertmanager configurations are exposed. Single-tenant deployments or setups where no one outside operators can write Alertmanager configs are less exposed. unknown whether managed Grafana Cloud is affected.
No product ranges from the sources yet.
mimir --version and confirm whether it is below 3.1.7 or 3.2.2.2.11 and 2.16, or below 2.17.20.3.1.7 or 3.2.2.2.17.20 or later; versions 2.11 through 2.16 will not receive a fix.Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
Grafana Mimir's Alertmanager rejects tenant-supplied receiver configurations that reference local files, but the check did not cover two HTTP client settings: http_headers.<name>.files and basic_auth.username_file. A tenant permitted to upload an Alertmanager configuration could point these fields at any file readable by the Alertmanager process. When a notification was sent, Alertmanager read the file and put its contents in a header of the outgoing request. By directing the receiver at a server they control, the tenant could read files from the Alertmanager host, such as credentials and configuration.
Exploitation requires permission to write the tenant's Alertmanager configuration. Grafana Enterprise Metrics (GEM), which is built on Mimir, is also affected. The issue is fixed in Mimir 3.1.7 and 3.2.2 and in GEM 2.17.20. GEM 2.11 through 2.16 will not receive a fix; users on those versions should upgrade to 2.17.20 or later.
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