Loki Path Traversal - CVE-2021-36156 Bypass

Answer in brief

CVE-2026-21726 records a Medium severity (CVSS 5.3) vulnerability in Loki Path Traversal - CVE-2021-36156 Bypass. The current sources do not mark it as known exploited. The current feed maps Grafana/Loki (generic), github.com/grafana/loki/v3 (go). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Apr 15, 2026Updated Sep 10, 2026Source checked Sep 25, 2026First seen by HOL Aug 11, 2026Material review Sep 10, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 5.3
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 5.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Grafana/Loki (generic), github.com/grafana/loki/v3 (go). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Grafana/Lokigeneric	>=2.3.0 <3.5.9	3.5.9
github.com/grafana/loki/v3go	>=0 <3.6.4	3.6.4

Recommended response

Check inventory. Check lockfiles and deployed manifests for Grafana/Loki, github.com/grafana/loki/v3.
Review the reported fix. Update Grafana/Loki to 3.5.9; github.com/grafana/loki/v3 to 3.6.4 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Apr 15, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 10, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 11, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.