---
title: "CVE-2023-38686\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-2023-38686?format=md
keywords: index, follow
---

# CVE-2023-38686

Publication date 4 August 2023

Last updated 4 August 2025

---

Ubuntu priority

**Medium**

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

## Cvss 3 Severity Score

**9.3 · Critical**

[Score breakdown](https://ubuntu.com/security/CVE-2023-38686?format=md#impact-score)

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## Description

Sydent is an identity server for the Matrix communications protocol. Prior
to version 2.5.6, if configured to send emails using TLS, Sydent does not
verify SMTP servers' certificates. This makes Sydent's emails vulnerable
to interception via a man-in-the-middle (MITM) attack. Attackers with
privileged access to the network can intercept room invitations and address
confirmation emails. This is patched in Sydent 2.5.6. When patching, make
sure that Sydent trusts the certificate of the server it is connecting to.
This should happen automatically when using properly issued certificates.
Those who use self-signed certificates should make sure to copy their
Certification Authority certificate, or their self signed certificate if
using only one, to the trust store of your operating system. As a
workaround, one can ensure Sydent's emails fail to send by setting the
configured SMTP server to a loopback or non-routable address under one's
control which does not have a listening SMTP server.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| matrix-sydent | 26.04 LTS resolute | Not in release |
| 25.10 questing | Not in release |
| 25.04 plucky | Not in release |
| 24.10 oracular | Ignored end of life, was needs-triage |
| 24.04 LTS noble | Needs evaluation |
| 23.10 mantic | Ignored end of life, was needs-triage |
| 23.04 lunar | Ignored end of life, was needed |
| 22.04 LTS jammy | Vulnerable |
| 20.04 LTS focal | Not in release |
| 18.04 LTS bionic | Not in release |
| 16.04 LTS xenial | Not in release |
| 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)

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

9.3 · Critical

* Base metrics

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

  | Parameter | Value |
  | --- | --- |
  | Base score | 9.3 · Critical |
  | Exploitability score | - |
  | Impact score | - |

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

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-38686)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2023-38686)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2023-38686)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2023-38686)

### Other references

* <https://github.com/matrix-org/sydent/pull/574>
* <https://github.com/matrix-org/sydent/commit/1cd748307c6b168b66154e6c4db715d4b9551261 (v2.5.6)>
* <https://github.com/matrix-org/sydent/security/advisories/GHSA-p6hw-wm59-3g5g>
* <https://github.com/python/cpython/issues/91826>
* <https://github.com/matrix-org/sydent/commit/1cd748307c6b168b66154e6c4db715d4b9551261>
* <https://github.com/matrix-org/sydent/releases/tag/v2.5.6>
* <https://peps.python.org/pep-0476/>
* <https://docs.python.org/3/library/ssl.html?highlight=ssl#security-considerations>
* <https://www.cve.org/CVERecord?id=CVE-2023-38686>