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CVE-2026-61666 – Denial of Service (Unhandled Exception) – websocket-driver-ruby < 0.8.2

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Summary

CVE-2026-61666 is a denial-of-service vulnerability in websocket-driver-ruby (the websocket-driver RubyGem maintained by Faye), caused by an uncaught URI::InvalidURIError exception when parsing a malformed Host header. The flaw affects WebSocket server implementations built on top of a raw TCP server using WebSocket::Driver.server(), and carries a severity score of 8.9 (High).

Technical details

  • Root cause: WebSocket::Driver.server() passes the client-supplied Host header directly to Ruby’s URI.parse without catching the URI::InvalidURIError exception (CWE-248: Uncaught Exception).
  • Trigger condition: A remote client sends a WebSocket handshake request with a Host header that does not conform to the expected host[:port] format.
  • Attack vector: Network — no authentication or user interaction is required; the malicious request can be sent directly to any exposed WebSocket endpoint using the vulnerable driver in TCP-server mode.
  • Impact: If the hosting application does not itself catch the exception raised from the driver’s parse() method, the unhandled error can crash the server process, resulting in a denial of service for the affected service.
  • No known workarounds exist other than upgrading; applications could theoretically wrap calls to the driver’s parse() method in their own exception handling, but this is not an officially endorsed mitigation.

Affected software

  • Product: websocket-driver-ruby (RubyGem: websocket-driver)
  • Vendor: Faye
  • Vulnerable versions: < 0.8.2
  • Fixed version: 0.8.2 and later

Severity

  • CVSS Score: 8.9 (High)
  • Vector (CVSS v4.0): CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
  • Key metrics: Network attack vector, low attack complexity, no privileges or user interaction required, high impact to availability, no impact to confidentiality or integrity.
  • Note: At the time of writing, this CVE has not yet been fully populated in the NVD database (record pending); the score above reflects the CVSS v4.0 vector published in the vendor’s GitHub Security Advisory.

Mitigation and recommended actions

  • Immediate: Upgrade websocket-driver to version 0.8.2 or later, where the request parser now catches URI::InvalidURIError and treats a malformed Host header as an invalid request, refusing to establish the WebSocket connection instead of crashing.
  • If immediate patching is not possible: Ensure the application layer wraps calls to the driver’s handshake/parsing methods in exception handling so an unexpected URI::InvalidURIError cannot propagate and crash the server process. This is a defense-in-depth measure only — no official workaround has been published, and upgrading remains the recommended fix.
  • Review dependency manifests (Gemfile/Gemfile.lock) for transitive use of websocket-driver via frameworks such as faye-websocket, em-websocket, or ActionCable, and confirm the resolved version is 0.8.2 or later.

References

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