Regular Expression Denial of Service in websocket-extensions (NPM package)

Impact

The ReDoS flaw allows an attacker to exhaust the server’s capacity to process
incoming requests by sending a WebSocket handshake request containing a header
of the following form:

Sec-WebSocket-Extensions: a; b="\c\c\c\c\c\c\c\c\c\c ...

That is, a header containing an unclosed string parameter value whose content is
a repeating two-byte sequence of a backslash and some other character. The
parser takes exponential time to reject this header as invalid, and this will
block the processing of any other work on the same thread. Thus if you are
running a single-threaded server, such a request can render your service
completely unavailable.

Patches

Users should upgrade to version 0.1.4.

Workarounds

There are no known work-arounds other than disabling any public-facing
WebSocket functionality you are operating.

References

• https://blog.jcoglan.com/2020/06/02/redos-vulnerability-in-websocket-extensions/