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https://issues.apache.org/jira/browse/MYFACES-4133?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16128817#comment-16128817
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Leonardo Uribe commented on MYFACES-4133:
-----------------------------------------

Encryption should NEVER be disabled for view state token, because there is no 
safe way to make it work with this disabled, but beyond that, I agree serialize 
the session id is not necessary on server side state saving. 

Please note encryption also adds a Message Authentication Code (MAC) that 
protects the view state token against tampering and other attacks, but this 
works together with the encryption.

It's more, maybe it is a good idea to change the default encryption algorithm 
to AES or something.

> Don't deserialize the ViewState-ID if the state saving method is server
> -----------------------------------------------------------------------
>
>                 Key: MYFACES-4133
>                 URL: https://issues.apache.org/jira/browse/MYFACES-4133
>             Project: MyFaces Core
>          Issue Type: Bug
>          Components: General
>    Affects Versions: 2.2.12
>            Reporter: Peter Stöckli
>
> Currently the ViewState-ID provided by the user is deserialized via Java 
> deserialization even when the {{javax.faces.STATE_SAVING_METHOD}} is set to 
> {{server}} (the default).
> The deserialization in this case is unecessary and most likely even slower 
> than just sending the ViewState Id directly.
> If a developer now disables the ViewState encryption by setting 
> {{org.apache.myfaces.USE_ENCRYPTION}} to {{false}} (against the [MyFaces 
> security advice|https://wiki.apache.org/myfaces/Secure_Your_Application]) he 
> might have unintentionally introduced a dangerous remote code execution (RCE) 
> vulnerability as described 
> [here|https://www.alphabot.com/security/blog/2017/java/Misconfigured-JSF-ViewStates-can-lead-to-severe-RCE-vulnerabilities.html].
> This has been discussed before on [Issue 
> MYFACES-4021|https://issues.apache.org/jira/browse/MYFACES-4021].



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