CVE-2007-4321

fail2ban 0.8 - Denial of Service via SSH Log File Parsing

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 1 public exploit for CVE-2007-4321. PoCs published by Daniel B. Cid.

AI-analyzed exploit summary This exploit demonstrates a denial-of-service vulnerability in Fail2ban by sending a crafted string to an SSH server, causing arbitrary IP addresses to be blocked. The PoC leverages the application's improper validation of authentication-failure messages.

Description

fail2ban 0.8 and earlier does not properly parse sshd log files, which allows remote attackers to add arbitrary hosts to the /etc/hosts.deny file and cause a denial of service by adding arbitrary IP addresses to the sshd log file, as demonstrated by logging in via ssh with a client protocol version identification containing an IP address string, a different vector than CVE-2006-6302.

Exploits (1)

exploitdb WORKING POC VERIFIED
by Daniel B. Cid · textdoslinux
https://www.exploit-db.com/exploits/30430

This exploit demonstrates a denial-of-service vulnerability in Fail2ban by sending a crafted string to an SSH server, causing arbitrary IP addresses to be blocked. The PoC leverages the application's improper validation of authentication-failure messages.

Classification
Working Poc 90%
Attack Type
Dos
Complexity
Trivial
Reliability
Reliable
Target: Fail2ban 0.8.0 and prior versions
No auth needed
Prerequisites: Network access to an SSH server monitored by Fail2ban
mistral-large-3 · analyzed Feb 16, 2026 Full analysis →

References (8)

Core 8
Core References
Third Party Advisory vendor-advisory x_refsource_debian
http://www.debian.org/security/2008/dsa-1456
Third Party Advisory third-party-advisory x_refsource_secunia
http://secunia.com/advisories/23237
Third Party Advisory, VDB Entry vdb-entry x_refsource_osvdb
http://osvdb.org/42484
Third Party Advisory, VDB Entry vdb-entry x_refsource_bid
http://www.securityfocus.com/bid/25117
Third Party Advisory third-party-advisory x_refsource_secunia
http://secunia.com/advisories/28374
Issue Tracking x_refsource_misc
http://bugs.gentoo.org/show_bug.cgi?id=181214
Third Party Advisory vendor-advisory x_refsource_gentoo
http://security.gentoo.org/glsa/glsa-200707-13.xml
Various Sources x_refsource_misc
http://www.ossec.net/en/attacking-loganalysis.html

Scores

EPSS 0.0575
EPSS Percentile 92.2%

Details

Status published
Products (1)
fail2ban/fail2ban 0.8
Published Aug 14, 2007
Tracked Since Feb 18, 2026