# CVE-2018-6556: The lxc-user-nic component of LXC allows unprivileged users to open arbitrary files

> Unprivileged users can open arbitrary files or special kernel files via lxc-user-nic, enabling path existence checks and potential side effects.

- **Severity:** Low 3.3 (`CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Aug 2018
- **Updated:** 17 Sep 2024
- **Also known as:** ALPINE-CVE-2018-6556, DEBIAN-CVE-2018-6556, GHSA-xg68-6jxg-5w7p, UBUNTU-CVE-2018-6556, USN-3730-1, openSUSE-SU-2019:1230-1

## What is CVE-2018-6556?

CVE-2018-6556 is a low-severity path traversal vulnerability in Canonical Ubuntu Linux, published on 10 Aug 2018. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

lxc-user-nic when asked to delete a network interface will unconditionally open a user provided path. This code path may be used by an unprivileged user to check for the existence of a path which they wouldn't otherwise be able to reach. It may also be used to trigger side effects by causing a (read-only) open of special kernel files (ptmx, proc, sys). Affected releases are LXC: 2.0 versions above and including 2.0.9; 3.0 versions above and including 3.0.0, prior to 3.0.2.

Weakness: CWE-417

## Which versions are affected by CVE-2018-6556?

It affects 6 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `lxc` | SUSE:Package Hub 15 | All versions | 2.0.9-bp150.5.6.1 |

Products: Canonical Ubuntu Linux, Linuxcontainers Lxc, Opensuse Leap, Suse Caas Platform, Suse Openstack Cloud, Suse Suse Linux Enterprise Server.

## How do I fix CVE-2018-6556?

Apply the vendor's patch.

## Is CVE-2018-6556 being exploited?

There is no known exploitation of CVE-2018-6556 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-6556 and fix it if it is affected.

What it is: CVE-2018-6556 is a low-severity path traversal vulnerability in Canonical Ubuntu Linux, published on 10 Aug 2018. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2018-6556 in the wild and no public exploit code.

Affected product: Canonical Ubuntu 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-2018-6556/ (Markdown: https://insights.sbomify.com/CVE-2018-6556/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-6556
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-6556
- OSV: https://osv.dev/vulnerability/CVE-2018-6556

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-6556/
Summaries are generated and may contain mistakes; the official description above is the record.