🚨 Regular Expression Denial of Service in websocket-extensions (RubyGem)

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.

Workarounds

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

0.1.5 (from changelog)

• Remove a ReDoS vulnerability in the header parser (CVE-2020-7663)

Does any of this look wrong? Please let us know.

See the full diff on Github. The new version differs by 6 commits:

• Bump version to 0.1.5
• Remove ReDoS vulnerability in the Sec-WebSocket-Extensions header parser
• Test on JRuby 9.{0,1,2} rather than "head"
• Update Ruby versions 2.4 to 2.7 on Travis
• Mention license change in the changelog
• Formatting change: {...} should have spaces inside the braces

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