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Fencer Vulns
medium 5.3

CVE-2026-21726 json

Loki Path Traversal - CVE-2021-36156 Bypass

published 2026-04-15 6 mo ago modified 2026-10-26 13 d ago also EUVD-2026-23100 , GHSA-497x-rrr9-68jp , GO-2026-5115

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 35%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/grafana/loki/v3 3.6.4
  • Grafana Loki 3.5.9
  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-21726 updated cvss 5.3

Loki: Loki: Information disclosure via path traversal vulnerability

  • Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/logging-loki-rhel9, openshift-logging/loki-rhel9-operator Red Hat Multicluster Global Hub multicluster-globalhub/multicluster-globalhub-grafana-rhel9 Red Hat Network Observability Operator network-observability/network-observability-rhel9-operator Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/acm-grafana-rhel9 Red Hat Ceph Storage 6 rhceph/rhceph-promtail-rhel9, rhceph/rhceph-6-dashboard-rhel9 Red Hat Enterprise Linux 8 grafana, grafana-loki, grafana-mssql, grafana-mysql, grafana-selinux, grafana-graphite, +8 more
    +2 more products
    Red Hat Enterprise Linux 9 grafana, grafana-selinux Red Hat OpenStack Platform 18.0 rhoso-operators/telemetry-rhel9-operator
    affected: no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.41% chance of exploitation in the next 30 days, higher than 35% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected packages

ecosystem package affected fixed in
go github.com/grafana/loki/v3
<3.6.4
3.6.4
go github.com/grafana/loki
all versions
 no fix listed

Affected products

  • Grafana Loki

Classification

Weakness
  • CWE-22 Improper Limitation of a Pathname to a Restricted Directory
  • CWE-601 URL Redirection to Untrusted Site

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.