The zero-day flaw in Flash Player that Adobe patched on Thursday targeted Microsoft Office users, according to security firm FireEye.
If your organisation is running Windows, Microsoft Office, and Flash Player, then Adobe’s Flash Player patch from last Thursday should be a top priority.
According to FireEye security researcher Genwei Jiang, Adobe rushed out a patch for Flash Player just four days after he reported that attackers were exploiting the bug (CVE-2016-4117).
Adobe said last week that it had received a report from FireEye that a zero-day bug for which it had no patch had been exploited in the wild, but besides disclosing that it could allow attackers to take control of a vulnerable system, it hadn’t it explained how the attack was deployed.
Adobe did however produce the patch quickly. Google offers vendors three months to patch any bug that it’s Project Zero team discovers before disclosing details about them.
FireEye’s Jiang has now detailed that the Flash exploit was embedded in a Microsoft Office document and that the attackers were targeting organisations that run Windows, Office and Flash.
The attackers sent booby-trapped Office files to targets in the hope that the file would be opened, however since they had also hosted the document on their own server, it could arrive as a link. If the target opened the document or the link, the exploit would be downloaded and executed from the attacker’s server.
Even though the attack didn’t rely on a vulnerability in any of Microsoft’s Office products, Office was a conduit to the user since it is able to render Flash files.
Oddly, it seems the attackers narrowed their tools to targets that had recently updated Flash Player.
According to Jiang, if the user was running a version of Flash Player older than 21.0.0.196 — which was released before April — the malware would abort the operation. For any new version of Flash, the exploit would run embedded native shellcode and then download a second piece of malware that displays a fake document.
FireEye’s Jiang recommended that enterprise users could consider deploying Microsoft’s Enhanced Mitigation Experience Toolkit (EMET) to make it more difficult for attackers to exploit this vulnerability. Otherwise, as Adobe has already recommended, Flash users should install the latest version of Flash Player immediately.
The Flash Player bug reported by FireEye was the third zero-day exploit in as many months that was being used by attackers before Adobe could patch the flaw.
It came as Google aired a plan to demote Flash Player as the default media player plugin in Chrome for all but the 10 most popular sites that require Flash to display content by the end of the 2016.