FireEye Labs recently spotted a 2011 article on cybercrime from the news site theguardian[.]com that redirects users to the Angler Exploit Kit. Successful exploitation by Angler resulted in a malware infection for readers of the article. A spokesperson for the guardian[.]com responded that they "are aware of FireEye's claims and are working to rectify the issue in question as soon as possible."
FireEye Labs first detected the activity on Dec. 1, 2015. Ironically, the affected article was titled “Cybercrime: is it out of control?” and covered various aspects of cybercrime. As it turns out, visiting the page shown in Figure 1 and Figure 2 silently redirected browsers to an Angler Exploit Kit landing page.
Figure 1. Article URL
Figure 2. Image from main page, highlighting cybercrime issues
The article loaded several other pages and links, including links for syndication shown in Figure 3 and Figure 4.
Figure 3. Sharing and syndication links
Figure 4. Syndication page URL
When the syndication link is loaded in the background, readers are eventually redirected to Angler’s landing page via injected HTML that crafts the request to the Angler landing page.
Visible in the HTML response is the script that would craft the URL to the Angler landing page. (Figure 5)
Figure 5. Injected script that loads the Angler landing page
Once loaded, the page would execute the embedded script and redirect the reader to the Angler landing page located at the URL in Figure 6:
Figure 6. Angler landing page URL
This redirect resulted in a new GET request (Figure 7) that loaded the landing page (Figure 8) and set up the exploitation stage.
Figure 7. Angler GET request, syndication link URL visible in Referrer field
Old exploits never die…
The use of an OLE Automation vulnerability exploited through VBScript, along with evidence of potential Flash exploitation, can be observed in this particular attack.
Angler unconditionally attempted to exploit a popular vulnerability: CVE-2014-6332. This is a memory corruption vulnerability in Windows Object Linking and Embedding (OLE) Automation, which can be triggered through VBScript with Internet Explorer as seen below.
The vulnerable code resided in OLEAUT32!SafeArrayRedim, where the original size of an array was not properly restored when an “Out of memory” error occured while resizing an array. This issue allowed for out-of-bounds memory access. In this attack the exploit was based on a publicly available PoC, and techniques from that PoC were used to attempt arbitrary code execution. Figure 8 shows Angler’s obfuscated version of the CVE-2014-6332 vulnerability trigger.
Figure 8. Angler landing page contents
Angler also unconditionally embedded a Flash object in the page at runtime. The FlashVars included crypto constants for D-H (g, u), and a URL to the payload (exec). Angler’s server then decided whether to serve a Flash exploit, presumably based on information in the request like x-flash-version.
The de-obfuscated object tag used to embed Flash movie files can be seen below in Figure 9:
Figure 9. Angler CVE-2014-6332 triggering function
It was common practice for Angler to decide which, if any, Flash exploit to deliver to the target at runtime. Most recently, we observed Angler delivering a number of high profile exploits. These included, but were not limited to, CVE-2015-5122, CVE-2015-5560, and CVE-2015-7645.
Typically, prior to conducting any exploitation on the system, Angler Exploit Kit attempted to detect whether Anti-Virus products or analysis tools are present. If Angler determined that such an object is present, it changed its behavior. For example, if Angler detected one such product, it invalidated its D-H parameters and the attack silently failed (Figure 10).
Another change bound to the presence of AV/analysis objects determines whether or not the malicious VBScript exploit is loaded. If detected, a non-malicious VBScript will be used instead. Or, it would if they remembered to unescape the string (Figure 11):
Figure 11. Return appropriate result based on the AV vendor check
This attack was discovered in FireEye Dynamic Threat Intelligence. Additional syndication URLs are also redirecting to Angler (Figure 12):
Figure 12. Constructing VBScript depending upon the presence of AV/analysis objects
Visitors to the site are encouraged to use caution to avoid potentially becoming infected.