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.

Threat Intelligence

5/15/2019
05:45 PM
50%
50%

Attackers Are Messing with Encryption Traffic to Evade Detection

Unknown groups have started tampering with Web traffic encryption, causing the number of fingerprints for connections using Transport Layer Security to jump from 19,000 to 1.4 billion in less than a year.

Online attackers are trying to obscure their encrypted traffic in an attempt to evade detection, using a technique known as "cipher stunting," accoding to Internet infrastructure and security firm Akamai.

Cipher stuffing modifies the fingerprint of communications encrypted with secure sockets layer (SSL) and transport layer security (TLS). Akamai, which fingerprints encrypted traffic as one way to identify attacks on its customers, found that the number of variations of the initial handshake request — known as the Client Hello packet — has recently exploded, from the usual thousands of variants in August 2018 to more than a billion in February. When used legitimately, each unique variant represents a different combination of encryption software, browser, operating system, and configuration of the encryption package. The change is on a "scale never seen before by Akamai," the company said in an analysis.

While variations could be due to legitimate software behavior or some sort of software defect, the most likely explanation is that attackers are attempting to evade detection or appear as a large number of different systems, says Moshe Zioni, director of threat research at Akamai.

"We were able to deduce with high certainty that it is a Java-based tool that made most of these permutations," he says. "The existence of such a thing means this was an intentional attempt to hide on the part of the threat actor … in the greater scheme, this is a good evasion technique."

The surge in variations of the Client Hello packets is the latest iteration of the cat-and-mouse game between attackers and defenders. Because SSL and TLS are so popular — 82% of malicious traffic uses encrypted communications, according to Akamai — many companies use fingerprinting as one of the techniques to classify traffic. Because the content of the communications is encrypted, defenders can only make use of the initial handshake between the client and server, which is in plaintext.

"This is a great illustration of one of the limitations of fingerprinting," says Shuman Ghosemajumder, chief technology officer of Shape Security, a website security firm. "If you are trying to fingerprint a device in any of many different ways, the first thing that an attacker will do is randomize that characteristic."

The goal for attackers is to make a single machine, or network of machines, look like hundreds of thousands or millions of users' devices, he says.

Fingerprinting encrypted communications using characteristics of the initial handshake between client and server is at least a decade old. In 2009, Qualys researcher Ivan Ristic described ways of fingerprinting clients and browsers from their SSL characteristics. In a talk at DerbyCon 2015, Lee Brotherston, at the time a senior security adviser at Leviathan Security Group, described how defenders could use TLS fingerprinting to better detect threats.

"The thing I like about TLS fingerprinting is that people don't tend to update how their crypto is set up that regularly. Even the big browsers with their regular releases have the same crypto between versions, and when I looked at malware, it never really changed their crypto signatures," Brotherston said at the time.

Akamai routinely looks at the initial Client Hello packets sent by a client as part of the process of establishing a secure connection between a browser client and a server. The packets allow anyone with access to the network to fingerprint, and later identify, a particular client. The fields included in the Client Hello packet are the TLS version, the session ID, cipher-suite options, and extensions and compression methods.

"Observing the way clients behave during the establishment of a TLS connection is beneficial for fingerprinting purposes so we can differentiate between attackers and legitimate users," Akamai stated in its analysis. "When we conduct fingerprinting, we aim to select components of the negotiation sent by all clients." 

Attackers are trying to pollute the waters. In August 2018, Akamai collected 18,652 distinct fingerprints on its global network, representing a fraction of a percent of all possible fingerprints. Starting in early September 2018, however, attackers started to randomize the characteristics of the cipher packets. By February of this year, the variation had hit 1.4 billion, the company stated.

Much of the randomization occurred on traffic attempting to use login credentials stolen from other sites to takeover accounts of Akamai clients.

With the explosion of random fingerprints, defenders will have problems classifying specific malware, but will still be able to detect TLS encryption requests that are behaving badly, Akamai's Zioni says.

"There is a relatively small and finite set of SSL/TLS stack implementations available today," he said. "We see strong correlation between randomization and malicious activity."

Related Content

 

 

 

Join Dark Reading LIVE for two cybersecurity summits at Interop 2019. Learn from the industry's most knowledgeable IT security experts. Check out the Interop agenda here.

Veteran technology journalist of more than 20 years. Former research engineer. Written for more than two dozen publications, including CNET News.com, Dark Reading, MIT's Technology Review, Popular Science, and Wired News. Five awards for journalism, including Best Deadline ... View Full Bio

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
Microsoft Patches Wormable RCE Vulns in Remote Desktop Services
Kelly Sheridan, Staff Editor, Dark Reading,  8/13/2019
The Mainframe Is Seeing a Resurgence. Is Security Keeping Pace?
Ray Overby, Co-Founder & President at Key Resources, Inc.,  8/15/2019
GitHub Named in Capital One Breach Lawsuit
Dark Reading Staff 8/14/2019
Register for Dark Reading Newsletters
White Papers
Video
Cartoon Contest
Write a Caption, Win a Starbucks Card! Click Here
Latest Comment: This comment is waiting for review by our moderators.
Current Issue
7 Threats & Disruptive Forces Changing the Face of Cybersecurity
This Dark Reading Tech Digest gives an in-depth look at the biggest emerging threats and disruptive forces that are changing the face of cybersecurity today.
Flash Poll
The State of IT Operations and Cybersecurity Operations
The State of IT Operations and Cybersecurity Operations
Your enterprise's cyber risk may depend upon the relationship between the IT team and the security team. Heres some insight on what's working and what isn't in the data center.
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2019-15150
PUBLISHED: 2019-08-19
In the OAuth2 Client extension before 0.4 for MediaWiki, a CSRF vulnerability exists due to the OAuth2 state parameter not being checked in the callback function.
CVE-2017-18550
PUBLISHED: 2019-08-19
An issue was discovered in drivers/scsi/aacraid/commctrl.c in the Linux kernel before 4.13. There is potential exposure of kernel stack memory because aac_get_hba_info does not initialize the hbainfo structure.
CVE-2017-18551
PUBLISHED: 2019-08-19
An issue was discovered in drivers/i2c/i2c-core-smbus.c in the Linux kernel before 4.14.15. There is an out of bounds write in the function i2c_smbus_xfer_emulated.
CVE-2017-18552
PUBLISHED: 2019-08-19
An issue was discovered in net/rds/af_rds.c in the Linux kernel before 4.11. There is an out of bounds write and read in the function rds_recv_track_latency.
CVE-2018-20976
PUBLISHED: 2019-08-19
An issue was discovered in fs/xfs/xfs_super.c in the Linux kernel before 4.18. A use after free exists, related to xfs_fs_fill_super failure.