The gang behind the CryptoDefense ransom malware has been distributing it using a simple Java drive-by attack as a way of boosting the number of victims, security firm Bromium has confirmed after analysing a version that appeared in March.
Although less well known than the rival CryptoLocker, CryptoDefense is more than a mere copycat program and shows an evolution beyond the former's incredibly successful design.
As well as employing powerful RSA-2048 bit encryption to scramble the victim's data, CryptoDefense targets source code as well as conventional data files, bypassing Windows Defender (in Windows 8) and disabling shadow and Windows restore to make it impossible to reinstate the files using that option.
A curious feature is that the gang behind CryptoDefense extended the 48-hour deadline to pay for an encryption key to as long as several weeks, presumably in a ploy to raise the number of people willing to pay.
When Symantec first documented the malware in March, its main distribution method was via email attachments, but that seems to have been complemented with more dangerous drive-by downloads targeting Java CVE-2012-4681 from 2012, which affects Java 7, update 6.
Bromium's analysis confirms that, as with Cryptolocker, drive-by infections have all along been a major way of infecting users. This might explain its success.
The stealthiness of drive-by attacks is that they usually require no user interaction and don't ask the user to click on a link or open an attachment. The example picked apart by Bromium didn't even require a privilege elevation, writing its code into a new process rather than piggybacking on one already running.
The malware's designers did make one major error that renders some earlier CryptoDefense infections reversible; the key used to encrypt files remains on the user's hard drive. Unfortunately, a version fixing this oversight has since appeared so the recovery instructions on crypto authority site Bleeping Computer won't work for everyone.
Exactly where Windows users stand in relation to this kind of malware is hard to assess. The element of surprise has gone for ransomware attackers and some have moved hack to conventional social engineering, rather than technically elaborate symmetric encryption keys to fuel their strong-arming.