---
title: "CVE-2018-21029\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-2018-21029?format=md
keywords: index, follow
---

# CVE-2018-21029

Publication date 30 October 2019

Last updated 4 August 2025

---

Ubuntu priority

**Low**

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

## Cvss 3 Severity Score

**9.8 · Critical**

[Score breakdown](https://ubuntu.com/security/CVE-2018-21029?format=md#impact-score)

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## Description

systemd 239 through 245 accepts any certificate signed by a trusted
certificate authority for DNS Over TLS. Server Name Indication (SNI) is not
sent, and there is no hostname validation with the GnuTLS backend. NOTE:
This has been disputed by the developer as not a vulnerability since
hostname validation does not have anything to do with this issue (i.e.
there is no hostname to be sent)

[Read the notes from the security team](https://ubuntu.com/security/CVE-2018-21029?format=md#notes)

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| systemd | 19.10 eoan | Not affected |
| 19.04 disco | Ignored end of life |
| 18.04 LTS bionic | Not affected |
| 16.04 LTS xenial | Not affected |
| 14.04 LTS trusty | Not affected |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)

## Notes

---

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

DNS over TLS not enabled by default in Ubuntu.
this is only an issue in v243 because strict mode got
introduced (DNSOverTLS=yes). Versions earlier than 243 only
implemented opportunistic mode which, according to specs,
might or not validate the resolver and can also be downgraded.

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

9.8 · Critical

* Base metrics

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

  | Parameter | Value |
  | --- | --- |
  | Base score | 9.8 · Critical |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-21029)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2018-21029)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2018-21029)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2018-21029)

### Other references

* <https://blog.cloudflare.com/dns-encryption-explained/>
* <https://github.com/systemd/systemd/blob/v243/src/resolve/resolved-dnstls-gnutls.c#L62-L63>
* <https://www.cve.org/CVERecord?id=CVE-2018-21029>