# CVE-2019-11479: Denial of service in Linux kernel

> Remote attackers can cause denial of service by fragmenting TCP resend queues due to a hard-coded small MSS in the Linux kernel.

- **Severity:** Medium 5.3 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Jun 2019
- **Updated:** 16 Sep 2024
- **Also known as:** DEBIAN-CVE-2019-11479, GHSA-99cq-xr7g-h22w, UBUNTU-CVE-2019-11479, USN-4041-1, USN-4041-2

## What is CVE-2019-11479?

CVE-2019-11479 is a medium-severity denial of service vulnerability in Canonical Ubuntu Linux, published on 18 Jun 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Jonathan Looney discovered that the Linux kernel default MSS is hard-coded to 48 bytes. This allows a remote peer to fragment TCP resend queues significantly more than if a larger MSS were enforced. A remote attacker could use this to cause a denial of service. This has been fixed in stable kernel releases 4.4.182, 4.9.182, 4.14.127, 4.19.52, 5.1.11, and is fixed in commits 967c05aee439e6e5d7d805e195b3a20ef5c433d6 and 5f3e2bf008c2221478101ee72f5cb4654b9fc363.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-405 (Asymmetric Resource Consumption (Amplification))

## Which versions are affected by CVE-2019-11479?

It affects 21 products.


Products: Canonical Ubuntu Linux, F5 Big-Ip Access Policy Manager, F5 Big-Ip Advanced Firewall Manager, F5 Big-Ip Analytics, F5 Big-Ip Application Acceleration Manager, F5 Big-Ip Application Security Manager, F5 Big-Ip Domain Name System, F5 Big-Ip Edge Gateway, F5 Big-Ip Fraud Protection Service, F5 Big-Ip Global Traffic Manager, F5 Big-Ip Link Controller, F5 Big-Ip Local Traffic Manager, F5 Big-Ip Policy Enforcement Manager, F5 Big-Ip Webaccelerator, F5 Big-Iq Centralized Management, F5 Enterprise Manager, F5 Iworkflow, F5 Traffix Signaling Delivery Controller, Linux kernel, Redhat Enterprise Linux and 1 more.

## How do I fix CVE-2019-11479?

Apply the vendor's patch.

## Is CVE-2019-11479 being exploited?

There is no known exploitation of CVE-2019-11479 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-2019-11479 and fix it if it is affected.

What it is: CVE-2019-11479 is a medium-severity denial of service vulnerability in Canonical Ubuntu Linux, published on 18 Jun 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2019-11479 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-2019-11479/ (Markdown: https://insights.sbomify.com/CVE-2019-11479/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-11479
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-11479
- OSV: https://osv.dev/vulnerability/CVE-2019-11479

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-11479/
Summaries are generated and may contain mistakes; the official description above is the record.