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https://issues.apache.org/jira/browse/ZOOKEEPER-2693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15872443#comment-15872443
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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_r101838329
--- Diff: src/java/main/org/apache/zookeeper/server/NIOServerCnxn.java ---
@@ -479,7 +479,7 @@ private boolean checkFourLetterWord(final SelectionKey
k, final int len)
// 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 (cmd == null ||
!FourLetterCommands.getWhiteListedCmdView().contains(cmd)) {
--- End diff --
I think the original comment was not clear but I think it is a good catch -
instead of return false here we return true because the semantic of
checkFourLetterWord is we only return false if 4lw is not found, and in that
case the caller will think this is a client message and proceed allocate buffer
etc work (iiuc that was what the "it should be processed in that way only"
meant.).
> 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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