Published about 1 month ago
Category: Denial of Service
Source: GitHub
Severity: Severe

Vulnerability in websocket-extensions


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.


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

CVSS Metrics
Access Vector Access Complexity Authentication Confidentiality Impact Integrity Impact Availability Impact
n/a n/a n/a n/a n/a n/a
Patched Versions

>= 0.1.5

Unaffected Versions