CVE-2020-15133
CVSS v3
8.7
HIGH
EPSS Score
1.1 %
exploit probability, as of 2026-09-26
CISA KEV
No
known exploited
Exploitation
—
SSVC status
Description
In faye-websocket before version 0.11.0, there is a lack of certification validation in TLS handshakes. The `Faye::WebSocket::Client` class uses the `EM::Connection#start_tls` method in EventMachine to implement the TLS handshake whenever a `wss:` URL is used for the connection. This method does not implement certificate verification by default, meaning that it does not check that the server presents a valid and trusted TLS certificate for the expected hostname. That means that any `wss:` connection made using this library is vulnerable to a man-in-the-middle attack, since it does not confirm the identity of the server it is connected to. For further background information on this issue, please see the referenced GitHub Advisory. Upgrading `faye-websocket` to v0.11.0 is recommended.
Technical details
- Published
- 2020-07-31
Frequently asked questions
What is CVE-2020-15133?
In faye-websocket before version 0.11.0, there is a lack of certification validation in TLS handshakes. The `Faye::WebSocket::Client` class uses the `EM::Connection#start_tls` method in EventMachine to implement the TLS handshake whenever a `wss:` URL is used for the connection. This method does not implement certificate verification by default, meaning that it does not check that the server presents a valid and trusted TLS certificate for the expected hostname. That means that any `wss:` connection made using this library is vulnerable to a man-in-the-middle attack, since it does not confirm the identity of the server it is connected to. For further background information on this issue, please see the referenced GitHub Advisory. Upgrading `faye-websocket` to v0.11.0 is recommended.
Is CVE-2020-15133 actively exploited?
Active exploitation of CVE-2020-15133 has not been confirmed. Its EPSS score was 1.1% on 2026-09-26, the estimated probability of exploitation in the next 30 days.
What is the CVSS score for CVE-2020-15133?
CVE-2020-15133 has a CVSS v3 base score of 8.7 (HIGH severity).
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