Inefficient regular expression complexity in Fail2ban - #VU153084
Published: October 1, 2026
Vulnerability identifier: #VU153084
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to inefficient regular expression complexity in the shared RFC5424 __prefix_line regex in common.conf when processing RFC5424 log lines containing unterminated structured-data fields. A remote attacker can inject a crafted RFC5424 log line to cause a denial of service.
Only filters configured with logtype=rfc5424 are affected.
Affected software
Fail2ban
Remediation
Install security update from vendor's website.
Fail2ban - update to 1.1.2