CVE-2020-15133: In faye-websocket before version 0.11.0, there is a lack of certification validation in TLS handshakes

Q: How do I fix CVE-2020-15133?

faye-websocket: upgrade to 0.11.0. Exact commands for each OS are on this page.

Q: Is CVE-2020-15133 being exploited?

CVE-2020-15133 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2020-15133 affect?

CVE-2020-15133 affects faye-websocket. Severity is high (CVSS 8.0). 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

Q: How urgent is CVE-2020-15133?

Priority 48/100. High severity; Public exploit reference

This month

HIGH 8.0UPGRADE

CVE-2020-15133 is a high-severity flaw (CVSS 8.0) affecting faye-websocket. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 ex

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.0 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.9% (top 40%)
CISA exploited list	No
Weakness	CWE-295
Published	2020-07-31
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: faye-websocket project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-07-31 18:15 UTCPublished CVE record published
2026-06-17 02:56 UTCUpdated Record last modified

faye-websocket project faye-websocket UPGRADE

Affected: < 0.11.0

Fixed in: 0.11.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy faye-websocket || rpm -q faye-websocket || faye-websocket --version

2. UPGRADE to 0.11.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade faye-websocket

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade faye-websocket

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-15133?

faye-websocket: upgrade to 0.11.0. Exact commands for each OS are on this page.

Is CVE-2020-15133 being exploited?

CVE-2020-15133 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-15133 affect?

CVE-2020-15133 affects faye-websocket. Severity is high (CVSS 8.0). 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

How urgent is CVE-2020-15133?

Priority 48/100. High severity; Public exploit reference

References

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