[UPDATE: 1/22/15: Adobe today issued an emergency patch for this vulnerability, and also is investigating yet another possible zero-day flaw (see Comments below)]
Prolific researcher Kafeine today called for Windows users to disable Adobe Flash Player in the wake of his discovery of an exploit for a previously unknown Flash flaw being packaged with a notorious crimeware kit.
A spokesperson for Adobe confirmed that the company was aware of the report and was investigating it.
Kafeine said in a blog post that he had seen one version of Angler EK sending three different attacks targeting Flash Player, one of which is a zero-day.
Malwarebytes has confirmed the validity of the zero-day exploit report. Pedro Bustamante, director of special projects for Malwarebytes, says the danger to Windows users, of course, is that there's no fix for the attack yet, and it's aimed at targeting machines "en masse."
"The fact that it has seemingly been integrated into the Angler Exploit Kit shows that criminals are keen to use it to target people and businesses en masse. Using a delivery mechanism such as Angler increases the chance of successful infections, allowing for accurate attacks through infected adverts on high-traffic websites," Bustamante says.
According to Malwarebytes security experts, the Angler Exploit Kit installs botnet malware for Bedep, a botnet that is able to load multiple payloads onto victim machines.
It's often used in drive-by download attacks to troll for certain vulnerabilities and then use them to drop malware, according to SANS Internet Storm Center director Johannes Ullrich. "This is still a developing story, but typically we see these exploits more in targeted attacks, not in widely used exploit kits. This flaw could affect a large number of users very quickly. Please refer to the original blog for details," Ullrich says in a blog post.
Kafeine as of this post was still testing vulnerable systems, but so far had found it exploiting Windows XP running Internet Explorer versions 6-9, Adobe Flash 126.96.36.1997; Windows 7 running IE8 and Flash 188.8.131.527; and Windows 8 running IE10 and Adobe Flash 184.108.40.206, for instance.
Up-to-date Windows 8.1 machines were unaffected, and he had not seen signs of Chrome being targeted.