Sydent does not verify email server certificates
Key facts
- Attack vector
- Adjacent network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Spoofing
- Confidentiality · integrity · availability
- High · High · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-295.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| matrix-org | sydent | before 2.5.6 | 2.5.6 | Patch available | CNA |
| — | matrix-sydent (PyPI) | before 2.5.6 | 2.5.6 | Patch available | GHSA-p6hw-wm59-3g5g |
- sydent Vendormatrix-org Affected before 2.5.6 Fixed in 2.5.6 Patch available CNA
- matrix-sydent (PyPI) Vendor— Affected before 2.5.6 Fixed in 2.5.6 Patch available GHSA-p6hw-wm59-3g5g
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:matrix:sydent:*:*:*:*:*:*:*:* | before 2.5.6 | Vulnerable | matrix-org |
- cpe:2.3:a:matrix:sydent:*:*:*:*:*:*:*:* Versions before 2.5.6 Vulnerable ·matrix-org
Remediation
- Fix · CNA sydent (matrix-org) Fixed in 2.5.6
- Fix · GHSA-p6hw-wm59-3g5g matrix-sydent (PyPI) Fixed in 2.5.6 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2023-38686
- 2026-10-03 Alias added: GHSA-p6hw-wm59-3g5g
References
Patch 2
Advisory 3
Other 6
- https://github.com/python/cpython/issues/91826
- https://docs.python.org/3/library/ssl.html?highlight=ssl#security-considerations
- https://github.com/matrix-org/sydent/releases/tag/v2.5.6
- https://github.com/matrix-org/sydent
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2023-139.yaml
- https://peps.python.org/pep-0476
More matrix-org Sydent vulnerabilities
- TI-2021-10144 SSRF in Sydent due to missing validation of hostnames CVSS 3.1HIGH 7.7
- TI-2021-10143 Denial of service attack via memory exhaustion CVSS 3.1HIGH 7.5
- TI-2019-08878 An issue was discovered in Matrix Sydent before 1.0.3 and Synapse before 0.99.3.1. CVSS 3.0HIGH 7.5
- TI-2019-08469 util/emailutils.py in Matrix Sydent before 1.0.2 mishandles registration restrictions… CVSS 3.0MEDIUM 5.9
- TI-2021-10145 Malicious users could control the content of invitation emails CVSS 3.1MEDIUM 5.7
- TI-2021-10146 Denial of service (via resource exhaustion) due to improper input validation CVSS 3.1MEDIUM 4.3
Sources
- CVE-2023-38686 · CVE Program
- CVE-2023-38686 · NVD
- FIRST EPSS
- GHSA-p6hw-wm59-3g5g · GitHub Advisory Database · CC BY 4.0
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