RubySec

Providing security resources for the Ruby community

CVE-2020-7663 (websocket-extensions): Regular Expression Denial of Service in websocket-extensions (RubyGem)

ADVISORIES

GEM

websocket-extensions

SEVERITY

CVSS v3: 7.5 (High)

PATCHED VERSIONS

  • >= 0.1.5

DESCRIPTION

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.