CVE-2023-38686

CVE-2023-38686 is a critical-severity vulnerability in Matrix Sydent with a CVSS 3.x base score of 9.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-295.

Key facts

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.

Frequently asked questions

What is CVE-2023-38686?
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.
How severe is CVE-2023-38686?
CVE-2023-38686 has a CVSS 3.x base score of 9.3, rated critical severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2023-38686 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-38686?
CVE-2023-38686 affects Matrix Sydent. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2023-38686?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2023-38686 published?
CVE-2023-38686 was published on 2023-08-04 and last updated on 2026-06-17.

References

Affected products (1)

More vulnerabilities in Matrix Sydent

All CVEs affecting Matrix Sydent →

Other CWE-295 (Improper Certificate Validation) vulnerabilities

Browse all CWE-295 (Improper Certificate Validation) vulnerabilities →