{"cve":"CVE-2023-38686","nvd":{"published":"2023-08-04T16:15:10.550","modified":"2026-06-17T06:10:57.123","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N","score":5.3},"cwes":["CWE-295"],"references":["https://docs.python.org/3/library/ssl.html?highlight=ssl#security-considerations","https://github.com/matrix-org/sydent/commit/1cd748307c6b168b66154e6c4db715d4b9551261","https://github.com/matrix-org/sydent/pull/574","https://github.com/matrix-org/sydent/releases/tag/v2.5.6","https://github.com/matrix-org/sydent/security/advisories/GHSA-p6hw-wm59-3g5g"],"products":["matrix:sydent"],"source":"nvd","synced_at":"2026-10-19T21:38:35.729974749+00:00"},"epss":{"cve":"CVE-2023-38686","score":0.00265,"percentile":0.1845,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-p6hw-wm59-3g5g","url":"https://osv.dev/vulnerability/GHSA-p6hw-wm59-3g5g","summary":"Sydent does not verify email server certificates","modified":"2026-09-10T03:49:42.620747023Z","packages":[{"ecosystem":"PyPI","name":"matrix-sydent","purl":"pkg:pypi/matrix-sydent","ranges":["<2.5.6"],"fixed":["2.5.6"]}]},{"id":"PYSEC-2023-139","url":"https://osv.dev/vulnerability/PYSEC-2023-139","summary":"","modified":"2023-11-08T04:13:09.175295Z","packages":[{"ecosystem":"PyPI","name":"matrix-sydent","purl":"pkg:pypi/matrix-sydent","ranges":["<2.5.6"],"fixed":["2.5.6"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}