CVE-2026-21726 | Loki Path Traversal - CVE-2021-36156 Bypass

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.

Published: 2026-04-15 Last update: 2026-04-20 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-21726 is rated Low Risk (32.9/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.41%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-21726

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.01% 0.41% +0.40%
2 2026-04-16 — 0.01% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-21726

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 [email protected]

Weakness enumeration for CVE-2026-21726

GitHub Security Advisory for CVE-2026-21726

GHSA-497x-rrr9-68jp · Severity: medium · Ecosystem: go — Grafana Loki Path Traversal - CVE-2021-36156 Bypass

OS Trackers for CVE-2026-21726

vendor priority summary link
alpine — CVE-2026-21726: 1 source package rows (loki); 29 state rows across 2 repos (3.23-community, edge-community); fixed 0, open 29. https://security.alpinelinux.org/vuln/CVE-2026-21726
redhat medium — https://access.redhat.com/security/cve/CVE-2026-21726
suse medium CVE-2026-21726 severity moderate: SUSE including 1 source package names (grafana), 4 product×package rows across 4 product lines (SUSE Linux Enterprise Module for Package Hub 15 SP7, SUSE Manager Client Tools for SLE 15, SUSE Multi-Linux Manager Client Tools for SLE 15, openSUSE Leap 15.6): Known Not Affected 4. https://www.suse.com/security/cve/CVE-2026-21726/

Affected software / configurations for CVE-2026-21726

Vendor Product Version Raw CPE
grafana loki < 3.6.4 cpe:2.3:a:grafana:loki:*:*:*:*:*:*:*:*

References for CVE-2026-21726

cvelogic Threat Intelligence