---
title: "CVE-2018-21035\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2018-21035?format=md
keywords: index, follow
---

# CVE-2018-21035

Publication date 28 February 2020

Last updated 26 August 2025

---

Ubuntu priority

**Low**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**8.6 · High**

[Score breakdown](https://ubuntu.com/security/CVE-2018-21035?format=md#impact-score)

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## Description

In Qt through 5.14.1, the WebSocket implementation accepts up to 2GB for
frames and 2GB for messages. Smaller limits cannot be configured. This
makes it easier for attackers to cause a denial of service (memory
consumption).

[Read the notes from the security team](https://ubuntu.com/security/CVE-2018-21035?format=md#notes)

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| qtwebsockets-opensource-src | 26.04 LTS resolute | Not affected |
| 25.10 questing | Not affected |
| 25.04 plucky | Not affected |
| 24.10 oracular | Not affected |
| 24.04 LTS noble | Not affected |
| 23.10 mantic | Not affected |
| 23.04 lunar | Not affected |
| 22.10 kinetic | Not affected |
| 22.04 LTS jammy | Not affected |
| 21.10 impish | Not affected |
| 21.04 hirsute | Not affected |
| 20.10 groovy | Ignored end of life |
| 20.04 LTS focal | Needs evaluation |
| 19.10 eoan | Ignored end of life |
| 18.04 LTS bionic | Needs evaluation |
| 16.04 LTS xenial | Needs evaluation |
| 14.04 LTS trusty | Not in release |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)
* [Patch details](https://ubuntu.com/security/CVE-2018-21035?format=md#patch-details)

## Notes

---

### [mdeslaur](https://launchpad.net/~mdeslaur)

upstream commit just adds new settings allowing users to lower
allowed frame/message size, it doesn't change the default
behaviour

### Patch details

For informational purposes only. We recommend not to cherry-pick updates. [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)

| Package | Patch details |
| --- | --- |
| qtwebsockets-opensource-src | * Upstream:   [ed93680](https://github.com/qt/qtwebsockets/commit/ed93680f34e92ad0383aa4e610bb65689118ca93) |

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

8.6 · High

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Changed |
  | Confidentiality impact | None |
  | Integrity impact | None |
  | Availability impact | High |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 8.6 · High |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-21035)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2018-21035)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2018-21035)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2018-21035)

### Other references

* <https://codereview.qt-project.org/c/qt/qtwebsockets/+/284735>
* <https://www.cve.org/CVERecord?id=CVE-2018-21035>