# CVE-2026-61666: faye websocket-driver-ruby denial of service via malformed Host header

Source: https://junglewise.ai/threats/cve-2026-61666-faye-websocket-driver-ruby-denial-of-service-via-malformed-host  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-17. Updated: 2026-07-21  
License: CC BY 4.0 with a link back

CVE-2026-61666 · Severity: high · CVSS 4 · Published 2026-08-17

A vulnerability in the websocket-driver-ruby library can allow a remote attacker to crash a WebSocket server. By sending a specially crafted request with a malformed Host header, an attacker can trigger an unhandled error that shuts down the server process. This results in a denial-of-service, making the application or service unavailable to legitimate users.

Technologies: [websocket-driver (RubyGems)](https://junglewise.ai/threats/technologies/websocket-driver). Vendors: [RubyGems](https://junglewise.ai/threats/vendors/rubygems).

## Quick answers

**Is CVE-2026-61666 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-61666 being exploited in the wild.

**How severe is CVE-2026-61666?** High severity, with a CVSS score of 4, published 17 August 2026.

**Which products and versions are affected?** Faye Project Websocket-Driver-Ruby < 0.8.2; websocket-driver (RubyGems) < 0.8.2, ECOSYSTEM:introduced=0,fixed=0.8.2.

**Is there a fix for CVE-2026-61666?** Yes. websocket-driver (RubyGems): upgrade to 0.8.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-61666 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-61666?** Check whether you run Faye Project Websocket-Driver-Ruby or websocket-driver (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- websocket-driver (RubyGems): upgrade to 0.8.2 or later

  ```sh
  bundle update websocket-driver
  ```


## Technical details

The vulnerability is an uncaught exception (CWE-248) in the `WebSocket::Driver.server()` method of the websocket-driver-ruby library. When the library parses an incoming WebSocket connection request, a malformed `Host` header that does not conform to the expected `host[:port]` format triggers a `URI::InvalidURIError`. If the calling application does not explicitly catch this error from the `parse()` method, the Ruby process will terminate. This can be exploited by a remote, unauthenticated attacker to cause a denial-of-service (DoS) condition. The issue is fixed in version 0.8.2 by ensuring the parser catches the exception and enters an error state instead of crashing.

## Affected products

- faye websocket-driver-ruby < 0.8.2

## Identifiers

- CVE-2026-61666
- GHSA-2x63-gw47-w4mm

## Timeline

- 2026-06-23: disclosed
- 2026-07-21: advisory: GitHub Advisory published
- 0.8.2: patched

## References

- [https://api.github.com/users/pranjalithakur](https://api.github.com/users/pranjalithakur)
- [https://github.com/pranjalithakur](https://github.com/pranjalithakur)
- [https://api.github.com/users/pranjalithakur/gists%7B/gist_id%7D](https://api.github.com/users/pranjalithakur/gists%7B/gist_id%7D)
- [https://api.github.com/users/pranjalithakur/repos](https://api.github.com/users/pranjalithakur/repos)
- [https://avatars.githubusercontent.com/u/47360190?v=4](https://avatars.githubusercontent.com/u/47360190?v=4)
- [https://api.github.com/users/pranjalithakur/events%7B/privacy%7D](https://api.github.com/users/pranjalithakur/events%7B/privacy%7D)

## Related threats

- [faye websocket-driver memory exhaustion in HTTP header parser](https://junglewise.ai/threats/cve-2026-54465-faye-websocket-driver-memory-exhaustion-in-http-header-parser)
- [Faye websocket-driver-ruby resource limit bypass in permessage-deflate](https://junglewise.ai/threats/cve-2026-54464-faye-websocket-driver-ruby-resource-limit-bypass-in-permessage)
- [faye websocket-driver-ruby memory exhaustion in draft protocol handler](https://junglewise.ai/threats/cve-2026-54463-faye-websocket-driver-ruby-memory-exhaustion-in-draft-protocol)