CVE-2023-38686Sydent does not verify email server certificates
- 9.3CriticalCVSS base score
- 0.27%Exploitation in 30 daysEPSS · top 81% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- YesPublic exploitsa reference or SSVC says so
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.
Public exploit
An exploit or proof of concept is public: anyone can try it against an unpatched system. CISA's SSVC rates its exploitation: a proof of concept is public.
Timeline
ID reserved
By GitHub_M
- 11 days later
· 11 days later
Published
- 14 months later
· 14 months later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Critical9.3 | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N |
| NVDNVD · Modified | 3.1 | Medium5.3 | CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |
- EPSS (exploitation in 30 days)
- 0.27% · top 81% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: poc · Automatable: no · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.3.
Affected products
- affected < 2.5.6
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- PyPImatrix-sydentGHSA-p6hw-wm59-3g5g (opens in a new tab)
References
References7
- https://github.com/matrix-org/sydent/security/advisories/GHSA-p6hw-wm59-3g5g (opens in a new tab)x_refsource_CONFIRMx_transferred
- https://github.com/python/cpython/issues/91826 (opens in a new tab)x_refsource_MISCx_transferred
- https://github.com/matrix-org/sydent/pull/574 (opens in a new tab)x_refsource_MISCx_transferred
- https://github.com/matrix-org/sydent/commit/1cd748307c6b168b66154e6c4db715d4b9551261 (opens in a new tab)x_refsource_MISCx_transferred
- https://docs.python.org/3/library/ssl.html?highlight=ssl#security-considerations (opens in a new tab)x_refsource_MISCx_transferred
- https://github.com/matrix-org/sydent/releases/tag/v2.5.6 (opens in a new tab)x_refsource_MISCx_transferred
- https://peps.python.org/pep-0476/ (opens in a new tab)x_refsource_MISCx_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2023-0132 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-p6hw-wm59-3g5g (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2023-38686)Record last updated .