HOMEVULNERABILITIESCVE-2021-41186
HIGH

CVE-2021-41186

CWE-400Published: October 29, 2021· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official 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).

NVD Source

Technical Analysis

CVE-2021-41186 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected Vendors & Products

fluentd1 product(s)
fluentd
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
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Official Patches & Advisories

ADVISORYhttps://github.com/fluent/fluentd/blob/master/CHANGELOG.md#v1142
ADVISORYhttps://github.com/fluent/fluentd/security/advisories/GHSA-hwhf-64mh-r662
ADVISORYhttps://github.com/fluent/fluentd/blob/master/CHANGELOG.md#v1142
ADVISORYhttps://github.com/fluent/fluentd/security/advisories/GHSA-hwhf-64mh-r662

All References (6)

→
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

Quick Facts

CVE IDCVE-2021-41186
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-400
CISA KEVNo
Affected1 vendor(s)
PublishedOct 29, 2021

Related CVEs (CWE-400)

CVE-2018-19282
9.8
CVE-2018-16489
9.8
CVE-2018-16492
9.8
CVE-2018-16491
9.8
CVE-2018-16486
9.8
CVE-2019-10952
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-41186 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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