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https://issues.apache.org/jira/browse/ZOOKEEPER-2693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15876398#comment-15876398
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ASF GitHub Bot commented on ZOOKEEPER-2693:
-------------------------------------------
Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/179#discussion_r102273810
--- 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 --
Thanks @arshadmohammad for your suggestion, I like this approach from a
user experience point of view as it provides nice error message on client side.
I am a little bit concerned that instead of doing a (nearly) NOP on server
side to block a command the way the patch is doing now (which just cost a look
up), any command including garbage now costs some string printing plus has to
go through network stack to send the bytes back. This may lead potential
vulnerable point, though it might also be OK as one could argue if we are in
such case (ZK server is wide open, every bets is off.). I tend to lean towards
the safer side though so I'll wait for a while for other comments regarding
this issue.
> 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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