IoT Inspector Research Lab Security Advisory IOT-20210311-0
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              title: Authenticated Command Injection in D-Link DIR-3060 Web 
                     Interface 
     vendor/product: D-Link DIR-3060 (https://www.dlink.com/)
 vulnerable version: v1.11b04 & Below
      fixed version: v1.11b04 Hotfix 2
         CVE number: CVE-2021-28144
             impact: 8.8 (high) CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
           reported: 2020-11-27
        publication: 2021-03-11
                 by: T Shiomitsu, IoT Inspector Research Lab
                     https://www.iot-inspector.com/

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Vendor description:
-------------------
D-Link Corporation is a Taiwanese multinational networking equipment 
manufacturing corporation. The DIR-3060 (also known as the EXO AC3000 Smart 
Mesh Wi-Fi Router) is one of their higher-end home/small business routers. 


Vulnerability overview/description:
-----------------------------------
The D-Link DIR-3060 is affected by a post-authentication command injection
vulnerability. Any person who is able to gain authenticated access to a 
DIR-3060 would be able to run arbitrary system commands on the device as the 
system "admin" user, with root privileges. 


Proof of concept:
-----------------
When a SOAP request is made to the SetVirtualServerSettings SOAP endpoint, the
function at 00461918 in prog.cgi is invoked. This function traverses the SOAP
XML request body, stores expected SOAP field values, and takes different paths
depending on the values. 

If a request with a non-null LocalIPAddress, Enabled set to “true”, an 
InternalPort of “9” and a ProtocolType of “UDP” is sent, the function 
CheckArpTables (named by me, based at 0046163c) is invoked.

// ...snip 
      iVar5 = strcmp(Enabled,"true"); 
      if ((((iVar5 == 0) && (LocalIPAddress != (char *)0x0)) && 
          (iVar5 = strcmp(InternalPort,"9"), iVar5 == 0)) && 
         (iVar5 = strcmp(ProtocolType,"UDP"), iVar5 == 0)) { 
        local_4154 = local_4154 + 1; 
        iVar5 = CheckArpTables(LocalIPAddress, InternalPort, ProtocolType, 0xdc, local_4154); 
        if (iVar5 == -1) { 
            local_4160 = 0xb; 
            goto LAB_00462504; 
        } 
      } 
// ...snip

Interestingly, UDP/9 correlates to the canonical Discard Protocol, which is the
TCP/UDP/IP equivalent of /dev/null. 

The CheckArpTables() function attempts to check the device ARP records, by 
calling the arp system command and grep’ing the output. However, the user-
controlled value passed as the LocalIPAddress is written directly into the 
command line format string with snprint(). This string is then passed directly
to a function called FCGI_popen(), which is a library function imported from 
libfcgi.so.

undefined CheckArpTables(char *LocalIPAddress, char *InternalPort, char *ProtocolType, undefined param_4, int param_5) {
    // ...snip...
    memset(buffer, 0, 0x40);
    // ...snip...
    snprintf(buffer, 0x40, "arp | grep %s | awk \'{printf $4}\'", LocalIPAddress);
    iVar1 = FCGI_popen(buffer, "r");
    // ...snip... 
}

We can see in libfcgi.so that FCGI_popen() is essentially only a thin wrapper 
around the stdio popen() library function. Arguments passed to FCGI_popen() 
get passed directly to popen().


int FCGI_popen(char *param_1, char *param_2) 
{
  FILE *__stream; 
  int iVar1; 
  __stream = popen(param_1,param_2); 
  iVar1 = FCGI_OpenFromFILE(__stream); 
  if ((__stream != (FILE *)0x0) && (iVar1 == 0)) { 
    pclose(__stream); 
  } 
  return iVar1; 
}

Since the LocalIPAddress value is not sanitized or checked in any way, a 
crafted command injection string can be passed as the LocalIPAddress, which 
will then be written to the arp command format string, and passed (almost) 
directly to popen(). 


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Vulnerable / tested versions:
-----------------------------
DIR-3060 v1.11b04


Solution:
---------
Apply D-Link-supplied patch, v1.11b04 Hotfix 2.


Advisory URL:
-------------
https://www.iot-inspector.com/blog/advisory-d-link-dir-3060/


Vendor contact timeline:
------------------------
2020-11-16: Initial contact made to ipsecure@dlinkcorp.com to request keys for 
            encryption.
2020-11-20: No reply received, so follow-up e-mail sent.
2020-11-27: No reply received, so advisory sent by e-mail without encryption.
2021-02-03: No reply received, so follow-up e-mail sent.
2021-02-12: No reply received, so inquiry sent using the forms at 
            support.dlink.com and eu.dlink.com/uk/en/contact-d-link.
2021-02-17: Response from the US D-Link support team, pointing us towards the 
            US-specific D-Link security page.
2021-02-17: Sent e-mail to this new US-specific D-Link security e-mail address.
2021-02-19: Response from a member of the D-Link USA SIRT.
2021-02-19: We request a public key from D-Link USA for transmission of the 
            advisory.
2021-02-19: PGP public key is provided by D-Link USA.
2021-02-19: Advisory is sent to D-Link USA with encryption.
2021-02-19: Receipt of advisory is confirmed by D-Link USA SIRT.
2021-02-19: We reply and ask for D-Link USA to keep us updated.
2021-02-20: D-Link “ipsecure” finally answers our e-mail, saying that 
            security@dlink.com should be the official e-mail, and the 
            ipsecure@dlinkcorp.com e-mail (the only one listed on the main 
            D-Link security disclosure page) is only a backup address.
2021-02-22: D-Link USA responds, confirming that the e-mail address listed 
            on the main D-Link security page has been changed.
2021-03-02: We e-mail D-Link USA to ask for a status update.
2021-03-02: D-Link USA responds with status update.
2021-03-08: D-Link USA provides patched firmware for testing.
2021-03-08: We respond asking for assigned CVE number.
2021-03-08: D-Link USA notes that they do not apply for, or manage CVE numbers
            related to their own products.
2021-03-08: We apply for a CVE number for this issue.
2021-03-08: D-Link USA publishes public advisory.
2021-03-11: CVE is assigned & IoT Inspector Research Lab publishes advisory.


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EOF T Shiomitsu / @2021