Impact

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.

Patches

v1.14.2

Workarounds

Either of the following:

• Don't use parser_apache2 for parsing logs which cannot guarantee generated by Apache.
• 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).

References

• CVE-2021-41186
• GHSA-hwhf-64mh-r662
• GHSL-2021-102
• https://github.com/fluent/fluentd/blob/master/CHANGELOG.md#v1142

References

• GHSA-hwhf-64mh-r662
• https://github.com/fluent/fluentd/blob/master/CHANGELOG.md#v1142
• https://github.com/github/securitylab-vulnerabilities/blob/52dc4a2a828c6dc24231967c2937ad92038184a9/vendor_reports/GHSL-2021-102-fluent-fluentd.md
• https://nvd.nist.gov/vuln/detail/CVE-2021-41186
• fluent/fluentd@5482a3d
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/fluentd/CVE-2021-41186.yml