CVE-2006-6302
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedfail2ban 0.7.4 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 login name containing certain strings with an IP address.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidencefail2ban versions 0.7.4 and earlier fail to properly parse sshd log files due to insufficient input validation. Attackers can authenticate to SSH with a specially crafted username containing an IP address, which fail2ban then misinterprets as a failed login from that IP, causing arbitrary IP addresses to be added to /etc/hosts.deny and resulting in denial of service.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 0.7.4CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Authentication
- None
- Confidentiality
- None
- Integrity
- None
- Availability
- Partial
AV:N/AC:L/Au:N/C:N/I:N/A:P
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Determine installed fail2ban versionRun 'fail2ban-client --version' or check the package manager (dpkg -l fail2ban, rpm -qi fail2ban)Affected if The version number returned is 0.7.4 or lower
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Verify SSH banning is activeCheck the fail2ban configuration in /etc/fail2ban/jail.conf or /etc/fail2ban/jail.local for the [ssh-iptables] or [ssh] section and confirm 'enabled = true'Affected if SSH jail is enabled and the fail2ban version is <= 0.7.4
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Inspect /etc/hosts.deny for unexpected IPsRun 'cat /etc/hosts.deny' and review the entries for any IP addresses that do not correspond to known failed login attemptsAffected if The file contains IP addresses that were not the result of legitimate failed SSH authentication attempts
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Examine SSH logs for crafted usernamesReview /var/log/auth.log (Debian) or /var/log/secure (RHEL/CentOS) for SSH login attempts where the username contains an IP address pattern (e.g., 'Invalid user 192.168.1.1')Affected if SSH logs contain login attempts with usernames that appear to be IP addresses, indicating exploitation attempts
You are affected if fail2ban version 0.7.4 or lower is installed with SSH banning enabled and either unexpected IPs appear in /etc/hosts.deny or crafted usernames are visible in SSH logs.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpgrade fail2ban to a version that properly validates and parses sshd log entries, or implement manual review/cleanup of /etc/hosts.deny to mitigate malicious entries.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2006-6302 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2006-6302 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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