Miscreants have deployed a subtle variant of the well established drive-by-download attack tactics against the website of human rights organisation Amnesty International.
In traditional drive-by-download attacks malicious code is planted on websites. This code redirects surfers to an exploit site, which relies on browser vulnerabilities or other exploits to download and execute malware onto visiting PCs.
The attack on the Amnesty website, detected by security firm Armorize, relied on a different sequence of events. In this case, malicious scripts are used to locate the malware which is already sitting in the browser's cache directory, before executing it.
This so-called drive-by cache approach make attacks harder to detect because no attempt is made to download a file and write it to disk, a suspicion manoeuvre many security software packages are liable to detect. By bypassing this step dodgy sorts are more likely to slip their wares past security software undetected.
The Amnesty International attack ultimately relied on an Adobe Flash zero-day exploit, patched by Adobe late last week, with the ultimate aim of dropping a backdoor on compromised machines.
A full write-up of the attack, analysing the code involved and explaining the concept of drive-by cache attacks in greater depth, can be found on the Armorize blog here.
It's at least the second time in six months Amnesty International's website has attacked its visitors. In November, visitors to the group's Hong Kong website were bombarded with a host of potent exploits, including one that targeted what was then a critical zero-day vulnerability in Internet Explorer. ®