CVE-2023-38686

Sydent SMTP TLS certificate verification vulnerability

• CVSS 5.3
• CWE-295 Improper Certificate Validation
• Cryptographic
• Remote

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.

CVE

CVE-2023-38686

CWE

CWE-295 Improper Certificate Validation

CVSS base score

5.3

Published

2023-08-04

OWASP

A05 Security Misconfiguration

Orthogonal defect classification

Checking

Code defect classification

Missing Check

Category

Cryptographic

Subcategory

Improper SSL/TLS Certificate Validation

Accessibility scope

Remote

Impact

Information Disclosure

Fixed by upgrading

Yes

Solution

Update to Sydent version 2.5.6 or higher.

import smtplib

def send_email(smtp_server, port, sender_email, receiver_email, message, use_tls=True):
    server = smtplib.SMTP(smtp_server, port)
    
    if use_tls:
        server.starttls()
    
    server.login(sender_email, 'your_password')
    server.sendmail(sender_email, receiver_email, message)
    server.quit()

import smtplib
import ssl

def send_email(smtp_server, port, sender_email, receiver_email, message, use_tls=True):
    context = ssl.create_default_context()
    
    with smtplib.SMTP(smtp_server, port) as server:
        if use_tls:
            server.starttls(context=context)
        server.login(sender_email, 'your_password')
        server.sendmail(sender_email, receiver_email, message)

@misc{vaitp:cve202338686,
  title        = {{Sydent SMTP TLS certificate verification vulnerability}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2023},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2023-38686},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2023-38686/}}
}