# CVE-2019-18198: Use after free in n/a

> A local attacker can exploit a reference count error in the Linux kernel IPv6 routing to corrupt memory, potentially leading to code execution or privilege escalation.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** No
- **Published:** 18 Oct 2019
- **Updated:** 5 Aug 2024
- **Also known as:** CVE-2021-3892, GHSA-3wc6-3hc2-3wc8, UBUNTU-CVE-2019-18198

## What is CVE-2019-18198?

CVE-2019-18198 is a high-severity use after free vulnerability in Canonical Ubuntu Linux, published on 18 Oct 2019. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel before 5.3.4, a reference count usage error in the fib6_rule_suppress() function in the fib6 suppression feature of net/ipv6/fib6_rules.c, when handling the FIB_LOOKUP_NOREF flag, can be exploited by a local attacker to corrupt memory, aka CID-ca7a03c41753.

Weakness: CWE-772 (Missing Release of Resource after Effective Lifetime)

## Which versions are affected by CVE-2019-18198?

It affects 2 products.


Products: Canonical Ubuntu Linux, Linux kernel.

## How do I fix CVE-2019-18198?

No fix has been published for CVE-2019-18198 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-18198 being exploited?

There is no known exploitation of CVE-2019-18198 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-2019-18198 and fix it if it is affected.

What it is: CVE-2019-18198 is a high-severity use after free vulnerability in Canonical Ubuntu Linux, published on 18 Oct 2019. 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-2019-18198 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-2019-18198/ (Markdown: https://insights.sbomify.com/CVE-2019-18198/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-18198
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-18198
- OSV: https://osv.dev/vulnerability/CVE-2019-18198

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-18198/
Summaries are generated and may contain mistakes; the official description above is the record.