Grafana Enterprise Metrics/Mimir Alertmanager http_headers..files/basic_auth.username_file information disclosure

Summaryinfo

A vulnerability labeled as problematic has been found in Grafana Enterprise Metrics and Mimir. This issue affects some unknown processing of the component Alertmanager. Such manipulation of the argument http_headers..files/basic_auth.username_file leads to information disclosure. This vulnerability is referenced as CVE-2026-81938. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Grafana Enterprise Metrics and Mimir (the affected version unknown). Affected by this issue is an unknown part of the component Alertmanager. The manipulation of the argument http_headers..files/basic_auth.username_file with an unknown input leads to a information disclosure vulnerability. Using CWE to declare the problem leads to CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. Impacted is confidentiality. CVE summarizes:

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.

The advisory is available at grafana.com. This vulnerability is handled as CVE-2026-81938 since 08/27/2026. The exploitation is known to be easy. The attack may be launched remotely. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1592 by the MITRE ATT&CK project.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• Grafana

Name

• Enterprise Metrics
• Mimir

License

• open-source

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