Attacks/Breaches
2/3/2017
02:45 PM
Connect Directly
Twitter
LinkedIn
RSS
E-Mail
50%
50%

Windows SMB Zero-Day Exploit On The Loose

Vulnerability allows remote attackers to trigger denial-of-service conditions on several Windows client versions.

US-CERT and other organizations Friday warned of a zero-day memory corruption bug in several versions of Microsoft Windows that could allow a remote attacker to cause a vulnerable system to crash and reboot.

Proof of concept code for exploiting the vulnerability has already been released on GitHub and is now publicly available for anyone to use. As of mid-day Eastern Time on Friday, no patch was available for the vulnerability, which poses more of threat for home and small businesses than enterprises.

The bug exists in the way certain Windows versions handle Server Message Block (SMB) traffic, Carnegie Mellon University’s CERT division said in an alert. By sending a specially crafted message from a malicious server, an attacker can trigger a buffer overflow condition in a vulnerable Windows system and cause it to crash, the alert noted. Several methods are available to attackers to get a Windows client system to connect to a malicious SMB server, sometimes with little to no user interaction, it added.

The Microsoft SMB file sharing protocol allows Windows clients to request services and to read and write files from Windows servers in a network. It has been the source of several security issues over the years.

A Microsoft spokesperson downplayed the severity of the issue. "Windows is the only platform with a customer commitment to investigate reported security issues, and proactively update impacted devices as soon as possible," the spokesperson said in a statement. "Our standard policy is that on issues of low risk, we remediate that risk via our current Update Tuesday schedule." 

Johannes Ullirch, head of the Internet Storm Center at the SANS Institute, said he tested the issue on a fully patched Windows 10 system using the proof of concept code and immediately got a blue screen of death. All Windows clients that support SMBv3 including Windows 2012 and 2016, appear vulnerable to the exploit, he said.

"The bug is a denial of service bug," Ullrich told Dark Reading. "If a system is hit by the exploit, then it will reboot." The bug does not appear to give attackers a way to execute code or do anything beyond triggering a denial of service condition.

Exploiting the vulnerability is easy, Ullrich says. The attacker can use the exploit to implement an SMBv3 server and then trick the victim into connecting to it. "The easiest way to accomplish this is by inserting a URL linking the server to a Web page," he says.

The URL might look like \\192.0.2.1\ipc$, where 192.0.2.1 is the IP address of the server. "An image tag like <img src=”[malicious url]”> will trigger the exploit."

The vulnerability is another reminder why it is necessary to block outbound SMB connections by blocking ports 445, 135 and 139, Ullrich says. "Many networks do not close these ports outbound, which opens up a number of attack possibilities, not just this one."

Home and small business users are more likely affected by the issue than enterprise users as small business and home firewalls usually do not block these connections by default, he notes.

In its advisory, CERT said it was currently unaware of a "practical solution" to the problem and urged organizations to block outbound SMB connections from the local network to the WAN on TCP ports 139 and 445 along with UDP ports 137 and 138.

Related Content:

 

Jai Vijayan is a seasoned technology reporter with over 20 years of experience in IT trade journalism. He was most recently a Senior Editor at Computerworld, where he covered information security and data privacy issues for the publication. Over the course of his 20-year ... View Full Bio

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
Register for Dark Reading Newsletters
White Papers
Video
Cartoon Contest
Write a Caption, Win a Starbucks Card! Click Here
Latest Comment: just wondering...Thanx
Current Issue
Security Operations and IT Operations: Finding the Path to Collaboration
A wide gulf has emerged between SOC and NOC teams that's keeping both of them from assuring the confidentiality, integrity, and availability of IT systems. Here's how experts think it should be bridged.
Flash Poll
New Best Practices for Secure App Development
New Best Practices for Secure App Development
The transition from DevOps to SecDevOps is combining with the move toward cloud computing to create new challenges - and new opportunities - for the information security team. Download this report, to learn about the new best practices for secure application development.
Slideshows
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2017-0290
Published: 2017-05-09
NScript in mpengine in Microsoft Malware Protection Engine with Engine Version before 1.1.13704.0, as used in Windows Defender and other products, allows remote attackers to execute arbitrary code or cause a denial of service (type confusion and application crash) via crafted JavaScript code within ...

CVE-2016-10369
Published: 2017-05-08
unixsocket.c in lxterminal through 0.3.0 insecurely uses /tmp for a socket file, allowing a local user to cause a denial of service (preventing terminal launch), or possibly have other impact (bypassing terminal access control).

CVE-2016-8202
Published: 2017-05-08
A privilege escalation vulnerability in Brocade Fibre Channel SAN products running Brocade Fabric OS (FOS) releases earlier than v7.4.1d and v8.0.1b could allow an authenticated attacker to elevate the privileges of user accounts accessing the system via command line interface. With affected version...

CVE-2016-8209
Published: 2017-05-08
Improper checks for unusual or exceptional conditions in Brocade NetIron 05.8.00 and later releases up to and including 06.1.00, when the Management Module is continuously scanned on port 22, may allow attackers to cause a denial of service (crash and reload) of the management module.

CVE-2017-0890
Published: 2017-05-08
Nextcloud Server before 11.0.3 is vulnerable to an inadequate escaping leading to a XSS vulnerability in the search module. To be exploitable a user has to write or paste malicious content into the search dialogue.

Dark Reading Radio
Archived Dark Reading Radio
In past years, security researchers have discovered ways to hack cars, medical devices, automated teller machines, and many other targets. Dark Reading Executive Editor Kelly Jackson Higgins hosts researcher Samy Kamkar and Levi Gundert, vice president of threat intelligence at Recorded Future, to discuss some of 2016's most unusual and creative hacks by white hats, and what these new vulnerabilities might mean for the coming year.