Re: ownCloud Unencrypted Private Key Exposure

From: Frank Stanek <>
Subject: Re: ownCloud Unencrypted Private Key Exposure


thank you for this announcement. I have a (very naive) question about 
this. As a consequence of this vulnerability an attacker with access to 
the ownCloud server's file system can compromise the encrypted data 
stored on the server. There does not seem to be a workaround for that 
and there will be no fix. Thus, data on an ownCloud server is always 
accessible to an attacker with access to the file system, regardless of 
whether ownCloud's encryption feature is enabled or not. Is that correct 
so far?

It seems to me that one of the encryption feature's main purposes is to 
prevent an attacker with access to the server's file system from 
immediate access to the user data. If my understanding above is true, 
then this purpose is void since the encryption is useless in that 
scenario. If this is somehow not part of the vendor's threat model, 
isn't it at least an important restriction? Or did I completely 
misunderstand something?


Am 04.08.2014 08:38, schrieb Senderek Web Security:
> Hash: SHA1
> Senderek Web Security - Security Advisory
> ownCloud Unencrypted Private Key Exposure
> =========================================
> Revision:         1.00
> Last Updated:     3 Aug 2014
> Summary:
>         In consequence of an insufficient threat model, ownCloud is
> storing all user's
>         private RSA keys in clear text in PHP session files.
>         These unencrypted private keys can be accessed by every web
> application that
>         has the privilege of the web server user. The affected files
> exposing cryptographic
>         keys will be stored in the PHP session directory for a number
> of hours until they
>         are removed.
>         This issue was reported to ownCloud via encrypted email on
> Tue, 11 Mar 2014.
>         I received a reply to this report from the vendor on Wed, 12
> Mar 2014.
>         On Tue, 22 July 2014 the vendor confirmed, that they will not
> address this problem,
>         because the protection of user encrypted files from remote
> attackers that have
>         read access to the file system with web server privilege is
> not - and will not be -
>         part of their threat model. Consequently, the vendor does not
> consider this to be
>         a vulnerability or security issue.
> Severity: High
> Affected Software Versions:
>         All versions of ownCloud since the introduction of the
> encryption module in
>         version 5.0.7 including version 7.0.0.
> Impact:
>         An attacker, who is able to read the PHP session files by
> exploiting another web
>         application that is running on the ownCloud server, will be
> able to gather the
>         unencrypted private key of every ownCloud user.
>         All encrypted files that are stored in a user's home
> directory can be decrypted
>         with this RSA private key, stored in the PHP session files in
> plain text.
>         If the user's encrypted files are synced to other devices or
> shared with
>         other servers - for hosting or backup - an attacker will be
> able to decrypt all
>         user data that is being intercepted, even if the attacker has
> no longer access to
>         the server's file system.
> Fixes:
>         In addition to the ownCloud encryption module users are
> advised to encrypt their
>         sensitive files separately with a standard server-side
> encryption mechanism like
>         GnuPG using a passphrase, that is not stored on the server
> except while being used
>         in memory.
>         One software solution that extends ownCloud with GnuPG-based
> server-side encryption
>         can be downloaded here:
>         A detailed installation tutorial is available at:
>         This general web application extension addresses a more
> comprehensive threat model,
>         that includes the possibility of read-access to web server
> accessible files on the
>         server. However, it does not protect against malicious
> actions of server admins,
>         as this cannot be prevented by web applications.
> Security Advice Policy:
>         Complete information about reporting security vulnerabilities
> can be found here:
>         All information in this security advisory is copyrighted
> because of the time and
>         effort in analysing and documenting the vulnerability 
> described here.
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