Skip to content
Fencer Vulns
medium 5.9

CVE-2021-41186 json

ReDoS vulnerability in parser_apache2

published 2021-10-29 5 y ago modified 2026-09-08 2 mo ago also BIT-fluentd-2021-41186 , EUVD-2021-2358 , GHSA-hwhf-64mh-r662

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.2%
EPSS 2.2% chance of exploitation in 30 days, percentile 82%
public exploits
0
none known

Summary

Fluentd collects events from various data sources and writes them to files to help unify logging infrastructure. The parser_apache2 plugin in Fluentd v0.14.14 to v1.14.1 suffers from a regular expression denial of service (ReDoS) vulnerability. A broken apache log with a certain pattern of string can spend too much time in a regular expression, resulting in the potential for a DoS attack. This issue is patched in version 1.14.2 There are two workarounds available. Either don't use parser_apache2 for parsing logs (which cannot guarantee generated by Apache), or put patched version of parser_apache2.rb into /etc/fluent/plugin directory (or any other directories specified by the environment variable `FLUENT_PLUGIN` or `--plugin` option of fluentd).

Patch / fix

  • rubygems fluentd 1.14.2
  • bitnami fluentd 1.14.2
  • rubygem-fluentd openSUSE Tumbleweed 1.17.1-1.5
  • rubygem-fluentd openSUSE Tumbleweed 1.17.1-1.3
  • rubygem-fluentd openSUSE Tumbleweed 1.17.0-1.1
  • rubygem-fluentd openSUSE Tumbleweed 1.14.4-1.1
  • ruby3.2-rubygem-fluentd openSUSE Tumbleweed 1.15.3-1.4

opensuse advisories openSUSE-SU-2026:10346-1openSUSE-SU-2025:15115-1openSUSE-SU-2024:14072-1openSUSE-SU-2024:11795-1openSUSE-SU-2024:13155-1

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-2021-41186 updated cvss 5.9

fluentd: ReDoS vulnerability in parser_apache2

  • Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/fluentd-rhel8
    affected: no fix planned “Will not fix”
  • Red Hat OpenShift Container Platform 3.11 fluentd Red Hat OpenShift Container Platform 4 openshift4/ose-logging-fluentd Red Hat OpenStack Platform 10 (Newton) puppet-fluentd Red Hat OpenStack Platform 10 (Newton) Operational Tools fluentd Red Hat OpenStack Platform 13 (Queens) puppet-fluentd Red Hat OpenStack Platform 13 (Queens) Operational Tools fluentd
    affected: no fix planned “Out of support scope”

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

Exploit prediction

2.21% chance of exploitation in the next 30 days, higher than 82% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
rubygems fluentd
>=0.14.14, <1.14.2
1.14.2
bitnami fluentd
>=0.14.14, <1.14.2
1.14.2

Affected products

  • fluent fluentd

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption

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.