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From "Michael Han (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2693) DOS attack on wchp/wchc four letter words (4lw)
Date Tue, 21 Feb 2017 22:32:44 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15876881#comment-15876881

Michael Han commented on ZOOKEEPER-2693:

bq. srvr is used in zookeeper/bin/zkServer.sh status
bq. isro is used in org.apache.zookeeper.ClientCnxn.SendThread.pingRwServer()

Good catch [~arshadmohammad] -  I hope this is an exhaustive list of 4lw used by ZK :) are
there other commands used by ZK itself if you may know?

Read only server is disabled by default, so we can leave isro out of white list by default
and document in admin manual that if read only server is enabled, this command must be put
back in white list. We can use a separate JIRA to get ride of isro from ZooKeeper client library

For srvr, it is only used in zkServer.sh's stat option - not sure if anyone actually use this
feature but we could just remove the Stat option from zkServer.sh so we don't have to include
srvr in whitelist. Another option is to include srvr in white list by default for 3.4/3.5.
I think include it by default in whitelist sounds the way to go from a compatibility point
of view.

> 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
>            Assignee: Michael Han
>            Priority: Blocker
>             Fix For: 3.4.10, 3.5.3
>         Attachments: ZOOKEEPER-2693-01.patch
> 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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