Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Vulnerabilities / Threats

4/9/2018
12:40 PM
Connect Directly
Twitter
LinkedIn
Google+
RSS
E-Mail
50%
50%

RTF Design, Office Flaw Exploited in Multi-Stage Document Attack

Threat actors chained CVE-2017-8570 with known design behaviors in .docx and RTF to launch a multi-stage document attack.

A newly discovered multi-stage document attack exploits design behaviors in .docx and RTF, along with CVE-2017-8570, to drop a malicious payload called Formbook on target endpoints. Attackers bypass traditional security tools with embedded URLs instead of active code.

Researchers at Menlo Security Labs who isolated the second-stage document say the behaviors enabling this attack are not new, but that this threat demonstrates an increasingly common way for hackers to slip past security defenses by relying on remotely hosted malicious objects.

"What we discovered is a new way in which Windows is getting the second-stage payload," says Vinay Pidathala, Menlo's director of security research. "There's absolutely no macros, no shellcode being used, just a URL. When the victim opens the document, it will go and fetch the remotely hosted components and load it in the context of the Word process."

The first stage of this attack is a phishing email with a malicious .docx file attached. The file does not have any macros, nor does it use any exploits, and embedded in its frame section is the URL. If the doc is opened, Word makes an HTTP request to download the remote object the URL is pointing to, which in this case redirects to another URL that points to a malicious RTF file.

Attackers are abusing capabilities in Microsoft Word that were more commonly used when it was an HTML editor, says Pidathala. Nobody uses Word to edit HTML anymore, he says, but those functions and API calls still exist and threat actors are taking advantage of them.

The RTF file contains an embedded script and another exploit, he continues. It marks stage two of the attack, which abuses both a design behavior in RTF documents and the CVE-2017-8570 vulnerability. When an RTF document with an embedded objected is opened, the object is automatically dropped into the %TEMP% directory of Windows.

"This is a well-documented design behavior, but we're seeing these getting abused by attackers now," he points out.

Half of the attack is achieved by dropping the malicious component on the endpoint, but it needs to be executed in order to fully compromise the machine. CVE-2017-8750 does this by executing the object to complete the attack and drop the Formbook malware.

Formbook, the final payload in this scenario, is a commercially available malware capable of taking screenshots, stealing personally identifiable information, keylogging, and downloading additional components if and when it needs to. Menlo researchers believe this is the first time Formbook has been delivered in this specific way.

While it's not a complete banking Trojan, Pidathala points out that it does have a banking component built into it. Full banking Trojans are solely built for stealing banking credentials; he describes this as "more like a RAT that has a lot of functionalities built into it."

This attack signifies a broader trend of threat actors leveraging remotely hosted objects to sneak past security defenses. In 2017, there were many zero-day exploits capable of fetching remote objects from the Internet and exploiting them in the context of Word, which researchers say was the only Office application used for this attack.

Now, attackers have begun to chain exploits with design behaviors to call remotely hosted malicious objects and run them without raising any red flags to the victim.

"All they have to do is open the first-stage document and that's pretty much it," says Pidathala, emphasizing the lack of user interaction needed to successfully launch the attack. "From there, they don't have to click anything or interact with the malicious document in any way."

It's difficult to tell an attack is taking place. "They're not able to identify anything malicious about it because all there is, is a reference to an external URL," says Menlo CTO Kowsik Guruswamy. "Technically it's not malicious; it's just a URL that happens to follow through with all the second- and third-stage droppers."

Related Content:

Interop ITX 2018

Join Dark Reading LIVE for two cybersecurity summits at Interop ITX. Learn from the industry’s most knowledgeable IT security experts. Check out the security track here. Register with Promo Code DR200 and save $200.

Kelly Sheridan is the Staff Editor at Dark Reading, where she focuses on cybersecurity news and analysis. She is a business technology journalist who previously reported for InformationWeek, where she covered Microsoft, and Insurance & Technology, where she covered financial ... View Full Bio
 

Recommended Reading:

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
COVID-19: Latest Security News & Commentary
Dark Reading Staff 9/25/2020
Hacking Yourself: Marie Moe and Pacemaker Security
Gary McGraw Ph.D., Co-founder Berryville Institute of Machine Learning,  9/21/2020
Startup Aims to Map and Track All the IT and Security Things
Kelly Jackson Higgins, Executive Editor at Dark Reading,  9/22/2020
Register for Dark Reading Newsletters
White Papers
Video
Cartoon
Current Issue
Special Report: Computing's New Normal
This special report examines how IT security organizations have adapted to the "new normal" of computing and what the long-term effects will be. Read it and get a unique set of perspectives on issues ranging from new threats & vulnerabilities as a result of remote working to how enterprise security strategy will be affected long term.
Flash Poll
How IT Security Organizations are Attacking the Cybersecurity Problem
How IT Security Organizations are Attacking the Cybersecurity Problem
The COVID-19 pandemic turned the world -- and enterprise computing -- on end. Here's a look at how cybersecurity teams are retrenching their defense strategies, rebuilding their teams, and selecting new technologies to stop the oncoming rise of online attacks.
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2020-15208
PUBLISHED: 2020-09-25
In tensorflow-lite before versions 1.15.4, 2.0.3, 2.1.2, 2.2.1 and 2.3.1, when determining the common dimension size of two tensors, TFLite uses a `DCHECK` which is no-op outside of debug compilation modes. Since the function always returns the dimension of the first tensor, malicious attackers can ...
CVE-2020-15209
PUBLISHED: 2020-09-25
In tensorflow-lite before versions 1.15.4, 2.0.3, 2.1.2, 2.2.1 and 2.3.1, a crafted TFLite model can force a node to have as input a tensor backed by a `nullptr` buffer. This can be achieved by changing a buffer index in the flatbuffer serialization to convert a read-only tensor to a read-write one....
CVE-2020-15210
PUBLISHED: 2020-09-25
In tensorflow-lite before versions 1.15.4, 2.0.3, 2.1.2, 2.2.1 and 2.3.1, if a TFLite saved model uses the same tensor as both input and output of an operator, then, depending on the operator, we can observe a segmentation fault or just memory corruption. We have patched the issue in d58c96946b and ...
CVE-2020-15211
PUBLISHED: 2020-09-25
In TensorFlow Lite before versions 1.15.4, 2.0.3, 2.1.2, 2.2.1 and 2.3.1, saved models in the flatbuffer format use a double indexing scheme: a model has a set of subgraphs, each subgraph has a set of operators and each operator has a set of input/output tensors. The flatbuffer format uses indices f...
CVE-2020-15212
PUBLISHED: 2020-09-25
In TensorFlow Lite before versions 2.2.1 and 2.3.1, models using segment sum can trigger writes outside of bounds of heap allocated buffers by inserting negative elements in the segment ids tensor. Users having access to `segment_ids_data` can alter `output_index` and then write to outside of `outpu...