CVE-2026-81938
HighCVSS 7.7Summary
Grafana Mimir's Alertmanager rejects tenant-supplied receiver configurations referencing local files, but the check did not cover http_headers.<name>.files and basic_auth.username_file. A tenant allowed to write the Alertmanager configuration could point these fields at any file readable by the process, and its contents were placed in a header of an outgoing request sent to an attacker-controlled server.
Risk Assessment
A tenant with configuration write permission could read files from the Alertmanager host, including credentials and configuration. Grafana Enterprise Metrics is also affected.
Recommendation
Upgrade Mimir to 3.1.7 or 3.2.2 and GEM to 2.17.20 or later; users on GEM 2.11 through 2.16 must upgrade to 2.17.20 or newer.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

