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Date: Mon, 20 Feb 2017 08:21:44 +0000 (UTC)
From: "ASF GitHub Bot (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (ZOOKEEPER-2693) DOS attack on wchp/wchc four
 letter words (4lw)
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archived-at: Mon, 20 Feb 2017 08:21:50 -0000


    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15874190#comment-15874190 ] 

ASF GitHub Bot commented on ZOOKEEPER-2693:
-------------------------------------------

Github user arshadmohammad commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/179#discussion_r101964775
  
    --- Diff: src/java/main/org/apache/zookeeper/server/NettyServerCnxn.java ---
    @@ -267,10 +267,17 @@ private boolean checkFourLetterWord(final Channel channel,
         {
             // We take advantage of the limited size of the length to look
             // for cmds. They are all 4-bytes which fits inside of an int
    -        String cmd = FourLetterCommands.getCmdMapView().get(len);
    -        if (cmd == null) {
    +        if (!FourLetterCommands.isKnown(len)) {
                 return false;
             }
    +
    +        // ZOOKEEPER-2693: don't execute 4lw if it's not enabled.
    +        String cmd = FourLetterCommands.getCommandString(len);
    +        if (!FourLetterCommands.isEnabled(cmd)) {
    +            LOG.debug("Command {} is not executed because it is not white listed.", cmd);
    +            return true;
    --- End diff --
    
    We can create a dummy command(ErrorCommand extends AbstractFourLetterCommand ) and execute it and return true same way as SetTraceMaskCommand 
    This ErrorCommand will take care rest of the thing, sending any error message to client and closing the connection etc. 


> 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
>
>
> 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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