# CVE-2013-6890: Denial of service in n/a

> Remote attackers can cause denial of service by blocking legitimate IP addresses via crafted login names due to flawed log parsing in denyhosts.

- **Severity:** Medium 5.0 (`AV:N/AC:L/Au:N/C:N/I:N/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:** 23 Dec 2013
- **Updated:** 6 Aug 2024
- **Also known as:** DSA-2826-1, GHSA-f4g4-953x-f5pm, MGASA-2014-0080

## What is CVE-2013-6890?

CVE-2013-6890 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 23 Dec 2013. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

denyhosts 2.6 uses an incorrect regular expression when analyzing authentication logs, which allows remote attackers to cause a denial of service (incorrect block of IP addresses) via crafted login names.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2013-6890?

It affects 3 products.


Products: Debian Debian Linux, Fedoraproject Fedora, Phil Schwartz Denyhosts.

## How do I fix CVE-2013-6890?

Upgrade to a fixed version.

## Is CVE-2013-6890 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2013-6890 exists.

Public exploit code:

- DenyHosts - 'regex.py' Remote Denial of Service (exploitdb)

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2013-6890 and fix it if it is affected.

What it is: CVE-2013-6890 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 23 Dec 2013. 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-2013-6890 exists.

Affected product: Debian Debian Linux. 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-2013-6890/ (Markdown: https://insights.sbomify.com/CVE-2013-6890/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2013-6890
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2013-6890
- OSV: https://osv.dev/vulnerability/CVE-2013-6890

---
From sbomify Insights: https://insights.sbomify.com/CVE-2013-6890/
Summaries are generated and may contain mistakes; the official description above is the record.