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CVE-2021-41186

ReDoS vulnerability in parser_apache2

HIGH
7.5
CVSS Score
Published: October 29, 2021 at 01:40 PM UTC
Updated: June 17, 2026 at 04:08 AM UTC
2 products affected across 2 vendorsFluentdFluentd

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Severity
HIGH7.5
Exploit prediction
EPSS 2%

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).

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Fluentd· Fluentd
95%
0.14.14 ≤ v ≤ 1.14.1
Fluentd· Fluent
60%
v < 1.14.2
Affected range stops below 1.14.2, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

References (3)

x_refsource_MISCRelease NotesThird Party Advisory
Source: [email protected]
https://github.com/fluent/fluentd/blob/master/CHANGELOG.md#v1142
x_refsource_CONFIRMThird Party Advisory
Source: [email protected]
https://github.com/fluent/fluentd/security/advisories/GHSA-hwhf-64mh-r662
x_refsource_MISCBroken Link
Source: [email protected]
https://github.com/github/securitylab-vulnerabilities/blob/52dc4a2a828c6dc24231967c2937ad92038184a9/vendor_reports/GHSL-2021-102-fluent-fluentd.md

CVSS

7.5HIGH[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-400

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