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Security Advisory: CSRF & DNS Changed Web Interface Attacks

 

TL;DR - Check the DNS settings on your DrayTek router and install new firmware.

 

In May 2018, we became aware of new attacks against web-enabled devices, which includes DrayTek routers. The recent attacks have attempted to change DNS settings of routers.  We are in the process of releasing updated firmware which you should upgrade to as soon as it is available but also immediately follow the advice below:

 

  1. Update your firmware immediately, or as soon as updated software is available. Before doing the upgrade, take a backup of your current config in case you need to restore it later (system maintenance -> Config backup).   Do use the .ALL file to upgrade, otherwise you will wipe your router settings.

  2. Check your DNS and DHCP settings on your router.   If you have a router supporting multiple LAN subnets, check settings for each subnet.  Your DNS settings should be either blank, set to the correct DNS server addresses from your ISP or DNS server addresses of a server which you have deliberately set (e.g. Google 8.8.8.8). A known rogue DNS server is 38.134.121.95 - if you see that, your router has been changed. 

    In the case of DHCP, the DHCP server may be disabled, which will typically cause errors on your LAN as devices fail to be issued with IP addresses so the problem is more obvious.




  3. If your settings appear to have been compromised, restore a config backup or manually check and correct all settings. Change your admin password and check that no other admin users have been added. Follow all of the advice in our previous CSRF article here.

  4. If you have remote access enabled on your router, disable it if you don't need it, and use an access control list if possible.   If you do not have updated firmware yet, disable remote access.  The ACL does not apply to SSL VPN connections (Port 443) so you should also temporarily disable SSL VPN until you have updated the firmware.



  5. Always use secured (SSL/TLS1.2) connections to your router, both LAN and WAN side. To do that, just prefix the address with https://.   Disabling non-SSL/TLS connections:



    The 'enable validation code' option at the top (above) is recommended. It adds a 'captcha' style option to the web admin login page.

  6. Report to us anything you find which looks suspicious. If you have syslog enabled (you can save syslogs to a USB stick on the router), send those to us securely. To make reports, UK users should use this link.

  7. If you are in the UK/Ireland, ensure that you're a member of our mailing list so that you can receive update and security advisories like this otherwise we have no way to notify you of this and any future issues. 

 

The priority for us has been to identify the cause and issue strengthened firmware so this is an initial report/advisory. We continue to monitor and investigate this issue and will update as appropriate.  At this stage, for obvious security reasons,  we will not be providing any further details of the issue.

 

Please share this advisory with other DrayTek users/SysAdmins.

Our firmware download page for UK/Irish users is here. For other regions, check your local DrayTek office or our HQ.  Firmware should start to be available from 18th May 2018 onwards (ETA). The very oldest models (>5 years) may not receive updates (TBA).

 

Our wireless access points (VigorAP series), switches (VigorSwitch series) and Vigor 2950, 2955, 2960, 3900 and 3300 series routers are not affected and do not need updating (but you should still always run the latest firmware on those anyway).   

 

Why would someone want to change my DNS anyway?

 

Changing your DNS server address might seem like a strange and very minor setting for a hacker to change but it is likely to be 'phase 1' of a larger attack.  A DNS server converts web addresses (like www.somewebsite.com) into an IP address (194.114.12.12 or 2001:db8::1) - the Internet router IP uses numeric addresses, not names. 

 

If someone can redirect you to a rogue DNS server, they can misdirect your browser to a fake site when you think you're going to your favourite web site. You login but now the criminals have your username and password (another reason people should use 2FA). The site will normally redirect you back to the genuine web site to avoid arousing suspicion.

 

At the time of writing, the known rogue address (38.134.121.95) is not responding to DNS queries so it may not have gone active yet, or the owner/operator of that address has now taken the compromised server offline. If your router was compromised, it will still work as the hackers set a secondary (legitimate) address of 8.8.8.8 (Google) as a fallback so that unavailability of their fake server didn't cause you to go and check your settings but don't leave it like that.

 

Keep up to Date via our Mailing List

 

It is always recommended that you keep your router and other hardware up to date with the latest firmware and read vendor mailing lists. We advise users of any critical or important issues like this one on the UK/Ireland mailing list and you are therefore encouraged to sign up here (For UK/Ireland users only - other regions, please check local resources).

 


Disclaimer : Please check this web page again for any new/updated information. You are advised to always keep your product's firmware or software up-to-date and keep in touch with your vendors to be advised of any new vulnerabilities (for example by subscribing to mailing lists). The information is this web page is provided in good faith based on the the information available to us at the current time, following an appropriate assessment but without acceptance of liability in the case of new, developing or existing threats or unlawful activity against your system. Any suggestions given above are provided as general information but should not be considered a thorough or specific assessment of your own individual security risks and you should take formal advice from a security expert to assess your specific security needs. As with any advisory, the suggested advice forms part of your own security planning and protocols.

Please note that mail alerts on this issue will come from our domain "drayteknews.co.uk" not our web domain (draytek.co.uk).  Both of the domains are legitimate and belong to us (DrayTek) but in line with anti-phishing measures, you're quite right to check.