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Re: ownCloud Unencrypted Private Key Exposure



Hi,

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?

Regards
Frank


Am 04.08.2014 08:38, schrieb Senderek Web Security:
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Senderek Web Security - Security Advisory

ownCloud Unencrypted Private Key Exposure
=========================================


https://senderek.ie/archive/2014/owncloud_unencrypted_private_key_exposure.php

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:

https://senderek.ie/downloads/release/cloud/wee-owncloud.tar

        A detailed installation tutorial is available at:

                https://senderek.ie/wee/cloud/wee-owncloud.php

        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:

                https://senderek.ie/responsible.disclosure.policy.php

        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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