# CVE-2007-4321: Denial of service in n/a

> Remote attackers can cause denial of service by injecting IP addresses into SSH logs, which fail2ban incorrectly parses into the hosts.deny file.

- **Severity:** Medium 6.8 (`AV:N/AC:M/Au:N/C:P/I:P/A:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 Aug 2007
- **Updated:** 7 Aug 2024
- **Also known as:** DEBIAN-CVE-2007-4321, DSA-1456-1, GHSA-5jfx-9p58-q8pj

## What is CVE-2007-4321?

CVE-2007-4321 is a medium-severity denial of service vulnerability in n/a, published on 14 Aug 2007. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

## Which versions are affected by CVE-2007-4321?

It affects 1 product.


Products: Fail2ban Fail2ban.

## How do I fix CVE-2007-4321?

Upgrade to a fixed version.

## Is CVE-2007-4321 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2007-4321 exists.

Public exploit code:

- Fail2ban 0.8 - Remote Denial of Service (exploitdb)

## Other vulnerabilities in n/a

- [CVE-2012-5642](https://insights.sbomify.com/CVE-2012-5642/): Command injection in n/a (high 7.5)
- [CVE-2021-32749](https://insights.sbomify.com/CVE-2021-32749/): Possible RCE vulnerability in mailing action using mailutils (mail-whois) (medium 6.1)
- [CVE-2013-7176](https://insights.sbomify.com/CVE-2013-7176/): Denial of service in n/a (medium 5.0)
- [CVE-2013-7177](https://insights.sbomify.com/CVE-2013-7177/): Denial of service in n/a (medium 5.0)
- [CVE-2013-2178](https://insights.sbomify.com/CVE-2013-2178/): Denial of service in n/a (medium 5.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2007-4321 and fix it if it is affected.

What it is: CVE-2007-4321 is a medium-severity denial of service vulnerability in n/a, published on 14 Aug 2007. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2007-4321 exists.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2007-4321/ (Markdown: https://insights.sbomify.com/CVE-2007-4321/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2007-4321
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2007-4321
- OSV: https://osv.dev/vulnerability/CVE-2007-4321

---
From sbomify Insights: https://insights.sbomify.com/CVE-2007-4321/
Summaries are generated and may contain mistakes; the official description above is the record.