CVE-2023-38686
CriticalCVSS 9.3Exploitation Probability (EPSS)
Low risk14th percentile - higher than 14% of all known CVEs
Summary
Sydent, an identity server for the Matrix communications protocol, prior to version 2.5.6, did not verify SMTP servers' certificates when sending emails using TLS. This makes Sydent's emails vulnerable to interception via a man-in-the-middle (MITM) attack.
Risk Assessment
Attackers with privileged access to the network can intercept room invitations and address confirmation emails, potentially leading to unauthorized access to information.
Recommendation
It is recommended to update Sydent to version 2.5.6 and ensure that Sydent trusts the certificate of the server it is connecting to. For those using self-signed certificates, the Certification Authority certificate should be copied to the trust store of the operating system.
Original NVD description (English source)
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.