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Date: Thu, 3 Mar 2011 01:44:36 +0000 (UTC)
From: "Sebb (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
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Subject: [jira] Updated: (NET-345) Telnet client: not properly handling IAC
 bytes within subnegotiation messages
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     [ https://issues.apache.org/jira/browse/NET-345?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sebb updated NET-345:
---------------------

    Fix Version/s: 3.0

> Telnet client: not properly handling IAC bytes within subnegotiation messages
> -----------------------------------------------------------------------------
>
>                 Key: NET-345
>                 URL: https://issues.apache.org/jira/browse/NET-345
>             Project: Commons Net
>          Issue Type: Bug
>          Components: Telnet
>    Affects Versions: 2.0
>            Reporter: Archie Cobbs
>             Fix For: 3.0
>
>         Attachments: patch3.txt, patch4.txt
>
>
> Subnegotiation messages in telnet are sent using the sequence {{IAC SB ... IAC SE}}.
> Although it's not clearly spelled out in [RFC 854|http://tools.ietf.org/html/rfc854], any {{IAC}} ({{0xff}}) bytes inside these messages must be escaped by doubling. Other clients do this and this is the only behavior that makes sense.
> The commons-net telnet client is failing both to escape and to unescape {{IAC}} bytes within subnegotiation messages. Moreover, if it does receive a valid {{IAC IAC}} sequence within a subnegotiation message, it will incorrectly jump back to "data" input mode, discarding the message and introducing its remainder as garbage in the data stream.
> In addition, the code fails to check for an overflow of the subnegotiation buffer, which would cause an {{ArrayIndexOutOfBounds}} exception if a malicious peer triggered this condition.
> Finally, a {{IAC SE}} sequence appearing by itself should probably be discarded, rather than passing as a command to the handler.
> I'm attaching a patch to fix these issues.

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