Grafana Loki Path Traversal - CVE-2021-36156 Bypass
Date: 2026-04
Affected: go/github.com/grafana/loki/v3
Attack vector: path-traversal
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-21726
CWE: CWE-22
CWE-601
CVSS: 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)

The CVE-2021-36156 fix validates the namespace parameter for path traversal sequences after a single URL decode, by double encoding, an attacker can read files at the Ruler API endpoint /loki/api/v1/rules/{namespace} Thanks to Prasanth Sundararajan for reporting this vulnerability.


Mitigations:

Architectural layers (MAESTRO):