CVE-2021-41186

Name: CVE-2021-41186
Creator: NVD / NIST
Published: 2021-10-29T14:15:07.73+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 2.06%

Last modified Jun 17, 2026

CVE-2021-41186 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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. EPSS estimates a 2.06% chance of exploitation in the next 30 days.

Description

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).

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

2.06%

78.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-400

Affected Software

Vendor	Product	Versions
Fluentd	Fluentd	>= 0.14.14, <= 1.14.1

References

https://github.com/fluent/fluentd/blob/master/CHANGELOG.md#v1142Release Notes, Third Party Advisory
https://github.com/fluent/fluentd/security/advisories/GHSA-hwhf-64mh-r662Third Party Advisory
https://github.com/github/securitylab-vulnerabilities/blob/52dc4a2a828c6dc24231967c2937ad92038184a9/vendor_reports/GHSL-2021-102-fluent-fluentd.mdBroken Link
https://github.com/fluent/fluentd/blob/master/CHANGELOG.md#v1142Release Notes, Third Party Advisory
https://github.com/fluent/fluentd/security/advisories/GHSA-hwhf-64mh-r662Third Party Advisory
https://github.com/github/securitylab-vulnerabilities/blob/52dc4a2a828c6dc24231967c2937ad92038184a9/vendor_reports/GHSL-2021-102-fluent-fluentd.mdBroken Link

Timeline

Published: Oct 29, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-41186?

How severe is CVE-2021-41186?

CVE-2021-41186 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 2.06% probability of exploitation in the next 30 days.

How do I fix CVE-2021-41186?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-41186?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST