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https://issues.apache.org/jira/browse/ZOOKEEPER-2693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15865958#comment-15865958
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Patrick Hunt commented on ZOOKEEPER-2693:
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I had another thought on how to handle this - rather than on/off we could limit
the number of 4lw that would be allowed to run in parallel. For example we
could allow only a single 4lw to run at any one time. This would still provide
the ability to run a 4lw, but with protection against overuse. It seems like
this should be fairly simple to implement. Additionally we could provide this
as an option (e.g. some folks might want to allow 5 to run in parallel).
Regardless if we take this approach I think we would still want the on/off
switches I already detailed.
> DOS attack on wchp/wchc four letter words (4lw)
> -----------------------------------------------
>
> Key: ZOOKEEPER-2693
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2693
> Project: ZooKeeper
> Issue Type: Bug
> Components: security, server
> Affects Versions: 3.4.0, 3.5.1, 3.5.2
> Reporter: Patrick Hunt
> Priority: Blocker
> Fix For: 3.4.10, 3.5.3
>
>
> The wchp/wchc four letter words can be exploited in a DOS attack on the ZK
> client port - typically 2181. The following POC attack was recently published
> on the web:
> https://webcache.googleusercontent.com/search?q=cache:_CNGIz10PRYJ:https://www.exploit-db.com/exploits/41277/+&cd=14&hl=en&ct=clnk&gl=us
> The most straightforward way to block this attack is to not allow access to
> the client port to non-trusted clients - i.e. firewall the ZooKeeper service
> and only allow access to trusted applications using it for coordination.
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