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Moab User Impersonation [CVE-2014-5375]

##[Moab User Impersonation : CVE-2014-5375]##

Software: Moab
Affected Versions: All current versions of Moab. However, the impact is limited 
in Moab 7.2.9 and Moab 8.
CVE Reference: CVE-2014-5375
Author: John Fitzpatrick, Luke Jennings MWR Labs 
(http://labs.mwrinfosecurity.com/)
Severity: High Risk
Vendor: Adaptive Computing
Vendor Response: Updates in Moab 7.2.9 and Moab 8 provide some mitigations


##[Description]

It is possible to submit jobs to Moab as arbitrary users due to insufficient 
authentication checks during the submission of a job to the Moab server.


##[Impact]
Users are able to submit jobs as arbitrary users. In environments that permit 
it this could allow job execution as root. 


##[Cause]

Moab does not sufficiently validate the job submissions against its intended 
user ID values.


##[Solution]

An upgrade to Moab 7.2.9 or Moab 8 prevents direct exploitation of this issue 
(further details are provided in the “Technical Details” section 
below). In these versions jobs submitted in this manner enter a held state, 
this is flagged as a known issue by Adaptive (MOAB-7478):

"Jobs submitted with invalid credentials are put in a held state, instead of 
rejected, until the administrator can respond. The checkjob command gives 
administrators further information regarding why the job is held. Blindly 
assuming that all held jobs should in fact be running RIGHT NOW is not only 
unsafe, but circumvents intentional Moab policies and workflow. An 
administrator should exercise care when resolving held jobs".

Administrators should be aware that attackers can control the <UserID> value 
which provides them control over the user specified within the checkjob. MWR 
would recommend that Adaptive make use of the &#147;actor&#148; value passed to 
Moab, as the controls introduced in 7.2.9 and 8 prevent manipulation of this 
value. 


##[Technical Details]

Moab is a workload manager used in High Performance Computing (HPC) 
environments. In a typical environment a user submits their jobs to the Moab 
server for it to handle the workload. Moab communication makes use of an XML 
based protocol. An example message showing a job submission is shown below:

<Envelope component="ClusterScheduler" count="1" name="moab" type="nonblocking" 
version="8.0.beta.2">
  <Signature>
    <DigestValue>7v49VzAlbyNQ4O3VChCus+v2LeE=</DigestValue>
    <SignatureValue>QG13cmxhYnMgRWFzdGVyIEVnZyE=</SignatureValue>
  </Signature>
  <Body actor="test" timestamp="1408488412">
    <Request action="submit" actor="test" cmdline="\STARTmsub">
      <Object>job</Object>
      <job>
        <Owner>test</Owner>
        <UserId>test</UserId>
        <GroupId>test</GroupId>
        <InitialWorkingDirectory>/home/test</InitialWorkingDirectory>
        <UMask>2</UMask>
        <Executable>/usr/bin/id</Executable>
        <SubmitLanguage>PBS</SubmitLanguage>
        <SubmitString>\START/usr/bin/id\0a\0a</SubmitString>
      </job>
    </Request>
  </Body>
</Envelope>

Within this message users are specified in multiple locations, these are 
highlighted in bold in the message above. In versions of moab prior to Moab 8 
there are two instances of the "actor" value specified. In order for mauth to 
sign a message the actor specified within the <Request> tag must match the user 
calling mauth. It is not necessary for the actor value within the <Body> tag to 
match the calling user.
In addition to checks at the mauth level the server will perform its own 
checks. The server ensures that the <Owner> matches the user specified within 
the <Body> actor value. If either differs an error (code 999 &#150; invalid 
credentials specified for submitted job) is returned by the server and the job 
rejected.

Since the actor value within the body tag is not verified by mauth, and this 
actor value is also the one against which the server checks the <Owner> tag, it 
is possible to smuggle through jobs to the server with an arbitrary user 
specified in each of these values. The user under which the job is queued by 
Moab is the user specified within the <UserId> tag. Whilst it is possible to 
impersonate a user by changing only this value, doing so appears to impede 
communication between Moab and a workload manager, on TORQUE this results in 
the job entering a BatchHold state where it will not execute. When the 
Body.actor value, the <Owner> and the <UserId> value are altered (but the 
Request.actor value remains legitimate to facilitate signing) it is possible to 
impersonate any user.

The example above describes this process when impersonating users during job 
submission. Moab also provides a means to reconfigure the server and a similar 
approach can be adopted to impersonate root and perform server reconfiguration.
In Moab 8 only a single actor value is contained within the messages and is 
used by both mauth and by the Moab server. This prevents manipulation of the 
<Owner> value during job submission. It remains possible to alter the <UserId> 
value and submit jobs in Moab 8 (as described above), although in a typical 
Moab+TORQUE configuration this does cause the job to enter a BatchHold state 
(other resource managers have not been tested).

Whilst components of this issue remain outstanding, upgrading to 7.2.9 or Moab 
8 appears to mitigate direct exploitation of the issue. 


##[Detailed Timeline]

2014-01-21 : Detailed vulnerability information provided to Adaptive 
2014-09-01 : Full advisory provided to Adaptive
2014-09-08 : Release of advisory to HPC community
2014-09-25 : Public release of advisory 


http://labs.mwrinfosecurity.com