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[jetty-announce] Eclipse Jetty DOS vulnerability for Quoted Quality CSV headers

Hello!


The Eclipse Jetty team wanted to make the community aware of a vulnerability discovered in recent versions of Jetty. This was given a CVE identifier of CVE-2020-27223.

Impact

When Jetty handles a request containing request headers with a large number of “quality” (i.e. q) parameters (such as what are seen on the `Accept`, `Accept-Encoding`, and `Accept-Language` request headers), the server may enter a denial of service (DoS) state due to high CPU usage while sorting the list of values based on their quality values.  A single request can easily consume minutes of CPU time before it is even dispatched to the application.


The only features within Jetty that can trigger this behavior are:


Default Error Handling - the `Accept` request header with the QuotedQualityCSV is used to determine what kind of content to send back to the client (html, text, json, xml, etc)


StatisticsServlet - uses the `Accept` request header with the QuotedQualityCSV to determine what kind of content to send back to the client (xml, json, text, html, etc)


HttpServletRequest.getLocale() - uses the `Accept-Language` request header with the QuotedQualityCSV to determine which “preferred” language is returned on this call.


HttpservletRequest.getLocales() - is similar to the above, but returns an ordered list of locales based on the quality values on the `Accept-Language` request header.


DefaultServlet - uses the `Accept-Encoding` request header with the QuotedQualityCSV to determine which kind of pre-compressed content should be sent back for static content (content that is not matched against a url-pattern in your web app)


Versions

QuotedQualityCSV was introduced to Jetty 9.3.9.v20160517 and the bug that introduced the vulnerability was in 9.4.6.v20170531. Currently, known vulnerable versions include:


  • 9.4.6.v20170531 thru to 9.4.36.v20210114

  • 10.0.0

  • 11.0.0

Workarounds

Quality ordered values are used infrequently by Jetty so they can be avoided:

  • Do not use the default error page/handler.

  • Do not deploy the StatisticsServlet exposed to the network

  • Do not call the getLocale or getLocales APIs

  • Do not include pre-compressed static content for the DefaultServlet to make the determination on

Alternately, a rewrite rule can be deployed to limit the number and size of Accept-* fields in the header.


Patches

All patches are available for download from the Eclipse Jetty website at https://www.eclipse.org/jetty/download.php

  • 9.4.37 and greater

  • 10.0.1 and greater

  • 11.0.1 and greater

Thank you,
The Eclipse Jetty Team


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