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

Status: published. Published: 2026-11-02. Updated: 2026-11-02.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Grafana / Enterprise Metrics (GEM): ≥ 2.11.0; ≤ 2.16.2 (affected, semver); ≥ 2.17.0; < 2.17.20 (affected, semver). Source: CNA: GRAFANA
- Grafana / Grafana Mimir: ≥ 3.0.4; < 3.1.7 (affected, semver); ≥ 3.2.0; < 3.2.2 (affected, semver). Source: CNA: GRAFANA

## Severity and prioritization

- CVSS 3.1: 7.7 (high); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N; source: CNA: GRAFANA

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-22

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://grafana.com/security/security-advisories/cve-2026-81938 (CNA: GRAFANA; vendor-advisory)

## Provenance

- CNA: GRAFANA: https://www.cve.org/CVERecord?id=CVE-2026-81938; retrieved 2026-11-02; source updated 2026-11-02

Revision: c309c2855b2a6d566b968b4f76bd3989398c48a1cfeb3e58a0fd2c60a6a33cb9

Canonical: https://y2.dev/cve/CVE-2026-81938

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