Adobe Flash Player Bug that can Leak Windows User Credentials

Adobe published a new version of Flash player in the middle of this week covering the Security issues under CVE-2017-3085 that affects all the platforms of windows(Windows XP, Vista, 7, 8.x and 10).

This flaw was identified by Security researcher Ruytenberg and it was derived from the old vulnerability(CVE-2016-4271) which Adobe patched on September 2016.

The previous flaw occurs in handling the input validation which leads to exfiltrate data and disclose them through SMB, and Adobe fixed the same with version 23 by dropping local-with-file-system sandbox and rejects UNC and File-style paths schemes (\\10.0.0.1\some\file.txt file://///10.0.0.1/some/file.txt.).

But Flaw with Input validation Continues

This new flaw identified by Ruytenberg and he published a Blog post on his work around with Flash Player’s new input validation, which restores an attacker’s ability to get Windows user credentials.

Also Read Adobe patches Multiple Security Flaw

Researches tried changing requested path after it gets passed the input validation after it and then redirects by using a know vulnerability Redirect-to-SMB which can be used in redirecting SMB requests to malicious servers.

They said Now, what if we could change the requested path after having passed input validation? Seeing as we are restricted to HTTP, this would translate to leveraging HTTP redirection for accessing SMB hosts.

From the results, they conclude Flash Player is not vulnerable to HTTP/1.1 302(Redirect-to-SMB), but they got a GETrequest for crossdomain.xml known as cross-domain policy file which controls when flash obtaining resource from different sources.

They said Interestingly, however, our Wireshark trace seemingly suggests otherwise: crossdomain.xml is being requested from the same host that serves our Flash application. Hence, we proceed by constructing a least-restrictive cross-domain policy.

They succeed by constructing a least-restrictive along SMBTrap that captures requests along with credentials.

Why Chrome and Edge not affected with Flash Player?

Chrome and Edge preventing flash from connecting over SMB hosts, so they are not vulnerable. On the other hand, Firefox and Internet Explorer remain vulnerable. Now the issues have been fixed with 26.0.0.151 fixes, users are recommended to update from Adobe’s website.