The recent ransomware attack on University College London has been discovered to have occurred as a result of an end user visiting a website hosting the Astrim exploit kit. Exploit kits are used to probe for vulnerabilities and exploit flaws to download malware.
Most ransomware attacks occur via email. Phishing emails are sent in the millions with many of those emails reaching end users’ inboxes. Ransomware is downloaded when infected email attachments are opened or malicious links are clicked. Organizations can reduce the threat of ransomware attacks by implementing an advanced spam filtering solution to prevent those malicious emails from being delivered.
However, spam filtering would not have stopped the University College London ransomware attack – one of many ransomware attacks on universities in recent months.
In order for an exploit kit to work, traffic must be sent to malicious websites hosting the kit. While spam email can be used to direct end users to exploit kits, the gang behind this attack was not using spam email.
The gang behind the Astrim exploit kit – AdGholas – has been using malvertising to direct traffic to sites hosting the EK. Malvertising is the name for malicious adverts that have been loaded onto third party ad networks. Those adverts are displayed to web users on sites that sign up with those advertising networks. Many high traffic sites display third party adverts, including some of the most popular sites on the Internet. The risk of employees visiting a website with malicious adverts is therefore considerable.
Exploit kit attacks are far less common than in 2015 and 2016. There was a major decline in the use of exploit kits such as Magnitude, Nuclear and Neutrino last year. However, this year has seen an increase in use of the Rig exploit kit to download malware and the Astrim exploit kit is also attempting to fill the void. Trend Micro reports that the Astrim exploit kit has been updated on numerous occasions in 2017 and is very much active.
The risk of exploit kit attacks is ever present and recent ransomware and malware attacks have shown that defenses need to be augmented to block malicious file downloads.
An exploit kit can only download malware on vulnerable systems. If web browsers, plugins and software are patched promptly, even if employees visit malicious websites, ransomware and malware cannot be downloaded.
However, keeping on top of patching is a difficult task given how many updates are now being released. Along with proactive patching policies, organizations should consider implementing a web filtering solution. A web filter can be configured to block third party adverts as well as preventing employees from visiting sites known to contain exploit kits.
With exploit kit attacks rising once again, now is the time to start augmenting defenses against web-based attacks. In the case of University College London, a fast recovery was possible as data were recoverable from backups, but that may not always be the case. That has been clearly highlighted by a recent ransomware attack on the South Korean hosting firm Nayana. The firm had made backups, but they too were encrypted by ransomware. The firm ended up paying a ransom in excess of $1 million to recover its files.