Sydent does not verify email server certificates

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.3 · CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

EPSS

• CVE-2023-38686: 0.27% estimated exploitation activity in the next 30 days; percentile 18.46 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact 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. CVSS 3.1 overall score: 3.3 - AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N/CR:L/IR:L/AR:X/MAV:A/MAC:H/MPR:N/MUI:N/MS:C/MC:L/MI:L/MA:N Reported by Martin Schobert, Pentagrid AG. Details Sydent can be configured to send emails over a TLS-encrypted socket by setting in its config file. Alternatively it can be configured to use Opportunistic TLS by setting In both situations, Sydent will encrypt its communication with the SMTP server when sending emails. In affected versions, Sydent will not verify the destination server's certificate. Vulnerability Sydent sends email for two purposes: - to inform a third party that they have been invited to a Matrix room by their email address; and - to verify that…

Published by the source

31 Jul 2023, 22:03 UTC

Last modified by the source

10 Sep 2026, 03:49 UTC

Source last checked

26 Oct 2026, 13:12 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-p6hw-wm59-3g5g

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-p6hw-wm59-3g5g

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# Patch Next advisory brief: CVE-2023-38686

Advisory: Sydent does not verify email server certificates
IDs: CVE-2023-38686, GHSA-p6hw-wm59-3g5g
Record: https://patchnext.com/advisories/cve-2023-38686 (revision 2, source checked 26 Oct 2026, 13:12 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-sydent 2.5.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI matrix-sydent: affected < 2.5.6; fixed in 2.5.6

## Suggested inspection (read-only)
- `python -m pip show matrix-sydent`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on matrix-sydent.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-p6hw-wm59-3g5g (OSV record GHSA-p6hw-wm59-3g5g lists affected ranges: PyPI matrix-sydent >=0 <2.5.6 (fixed))
- Verified: https://github.com/advisories/GHSA-p6hw-wm59-3g5g (GitHub-reviewed advisory GHSA-p6hw-wm59-3g5g lists affected ranges: PyPI matrix-sydent >=0 <2.5.6)

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