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

4/3/2018
05:30 PM
Connect Directly
Twitter
LinkedIn
Google+
RSS
E-Mail
50%
50%

New Attack Vector Shows Dangers of S3 Sleep Mode

Researchers at Black Hat Asia demonstrated how they can compromise the security of a machine as it powers down and wakes up.

Two researchers at Black Hat Asia last month gave computers a reason to sleep with one eye open in their demo of "S3 Sleep," a new attack vector used to subvert the Intel Trusted eXecution Environment (TXT). A flaw in Intel TXT lets hackers compromise a machine as it wakes up.

Intel TXT is the hardware-based functionality that supports the dynamic root-of-trust measurement (DRTM) and validates the platform's trustworthiness during boot and launch. This attack targets trusted boot (tBoot), a reference implementation of Intel TXT normally used in server environments. tBoot is an open-source project that protects the virtual machine monitor (VMM) and operating system.

Senior security researcher Seunghun Han and security researcher Jun-Hyeok Park, both with the National Security Research Institute of South Korea, presented an exploit of the "Lost Pointer" vulnerability (CVE-2017-16837), a software flaw in tBoot. This specific attack vector has never been reported, the two said at Black Hat, and attackers only need root privilege to do it.

Researchers have investigated Intel TXT and tBoot before, the researchers explained. However, previous studies have only focused on the boot process. This one focuses on the sleeping and waking up sequence of tBoot, and how attackers could exploit a machine as it reactivates.

Securing the sleep states

Sure, you could avoid this kind of attack by keeping machines running constantly, so Han started their Black Hat session by pointing out the financial reasons for sleep mode. "Power consumption is cost," Han explained. "Many companies worry about power consumption for their products because lower power consumption means a lower electricity fee."

Shutting down machines dramatically reduces power consumption; however, reactivating all of their components poses a security risk. As the computer wakes up, restarting its many parts takes time and security devices might be temporarily shut down for part of the process.

PC, laptop, and server environments supporting advanced configuration and power interface (ACPI) have six sleeping states to gradually reduce power consumption as the machine shuts down. The states go from S0 to S5 as the CPU, devices, and RAM go into full sleep mode. Power to the CPU and devices is cut off at the S3 phase of sleep.

"Because of power-off, their states need to be restored and reinitialized for waking up," says Han. "If we intercept sleep and waking up, we can do something interesting."

There are boot protection mechanisms, Park says. The secure boot of the Unified Extensible Firmware Interface (UEFI) checks a cryptographic signature of the binary prior to execution, and stops it if the executable file lacks a valid signature. "Measured boot" measures a hash of the binary prior to execution and stores the measurement to the Trusted Platform Module (TPM).

TPM is a hardware security device widely deployed in commercial devices, Han says. It's designed with a random number generator, encryption functions, and Platform Configuration Registers (PCRs), which store hashes and can be used to seal data like Bitlocker, he explains.

The danger of sleep mode

When the system wakes up, it should turn on the security functions of the CPU and recover the PCRs of the TPM. However, because of the Lost Pointer flaw, tBoot doesn't measure all function pointers. Certain pointers in tBoot are not validated and can cause arbitrary code execution.

By exploiting the Lost Pointer flaw on a machine in S3 sleep mode, Han and Park found they can forge PCR values while a system sleeps and wakes up. If they can make the PCR variables whatever they want, attackers can subvert the Intel TXT security mechanism.

The researchers advise updating your tBoot to the latest version, or disabling the sleep feature in the BIOS, to protect against this kind of attack.

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

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
7 Truths About BEC Scams
Ericka Chickowski, Contributing Writer,  6/13/2019
DNS Firewalls Could Prevent Billions in Losses to Cybercrime
Curtis Franklin Jr., Senior Editor at Dark Reading,  6/13/2019
Can Your Patching Strategy Keep Up with the Demands of Open Source?
Tim Mackey, Principal Security Strategist, CyRC, at Synopsys,  6/18/2019
Register for Dark Reading Newsletters
White Papers
Video
Cartoon
Current Issue
Building and Managing an IT Security Operations Program
As cyber threats grow, many organizations are building security operations centers (SOCs) to improve their defenses. In this Tech Digest you will learn tips on how to get the most out of a SOC in your organization - and what to do if you can't afford to build one.
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-2019-2729
PUBLISHED: 2019-06-19
Vulnerability in the Oracle WebLogic Server component of Oracle Fusion Middleware (subcomponent: Web Services). Supported versions that are affected are 10.3.6.0.0, 12.1.3.0.0 and 12.2.1.3.0. Easily exploitable vulnerability allows unauthenticated attacker with network access via HTTP to compromise ...
CVE-2019-3737
PUBLISHED: 2019-06-19
Dell EMC Avamar ADMe Web Interface 1.0.50 and 1.0.51 are affected by an LFI vulnerability which may allow a malicious user to download arbitrary files from the affected system by sending a specially crafted request to the Web Interface application.
CVE-2019-3787
PUBLISHED: 2019-06-19
Cloud Foundry UAA, versions prior to 73.0.0, falls back to appending ?unknown.org? to a user's email address when one is not provided and the user name does not contain an @ character. This domain is held by a private company, which leads to attack vectors including password recovery emails sent to ...
CVE-2019-12900
PUBLISHED: 2019-06-19
BZ2_decompress in decompress.c in bzip2 through 1.0.6 has an out-of-bounds write when there are many selectors.
CVE-2019-12893
PUBLISHED: 2019-06-19
Alternate Pic View 2.600 has a User Mode Write AV starting at PicViewer!PerfgrapFinalize+0x00000000000a8868.