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.

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
 

Recommended Reading:

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
Commentary
How SolarWinds Busted Up Our Assumptions About Code Signing
Dr. Jethro Beekman, Technical Director,  3/3/2021
News
'ObliqueRAT' Now Hides Behind Images on Compromised Websites
Jai Vijayan, Contributing Writer,  3/2/2021
News
Attackers Turn Struggling Software Projects Into Trojan Horses
Robert Lemos, Contributing Writer,  2/26/2021
Register for Dark Reading Newsletters
White Papers
Video
Cartoon Contest
Current Issue
2021 Top Enterprise IT Trends
We've identified the key trends that are poised to impact the IT landscape in 2021. Find out why they're important and how they will affect you today!
Flash Poll
How Enterprises are Developing Secure Applications
How Enterprises are Developing Secure Applications
Recent breaches of third-party apps are driving many organizations to think harder about the security of their off-the-shelf software as they continue to move left in secure software development practices.
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2021-26788
PUBLISHED: 2021-03-08
Oryx Embedded CycloneTCP 1.7.6 to 2.0.0, fixed in 2.0.2, is affected by incorrect input validation, which may cause a denial of service (DoS). To exploit the vulnerability, an attacker needs to have TCP connectivity to the target system. Receiving a maliciously crafted TCP packet from an unauthentic...
CVE-2021-23351
PUBLISHED: 2021-03-08
The package github.com/pires/go-proxyproto before 0.5.0 are vulnerable to Denial of Service (DoS) via the parseVersion1() function. The reader in this package is a default bufio.Reader wrapping a net.Conn. It will read from the connection until it finds a newline. Since no limits are implemented in ...
CVE-2009-20001
PUBLISHED: 2021-03-07
An issue was discovered in MantisBT before 2.24.5. It associates a unique cookie string with each user. This string is not reset upon logout (i.e., the user session is still considered valid and active), allowing an attacker who somehow gained access to a user's cookie to login as them.
CVE-2020-28466
PUBLISHED: 2021-03-07
This affects all versions of package github.com/nats-io/nats-server/server. Untrusted accounts are able to crash the server using configs that represent a service export/import cycles. Disclaimer from the maintainers: Running a NATS service which is exposed to untrusted users presents a heightened r...
CVE-2021-27364
PUBLISHED: 2021-03-07
An issue was discovered in the Linux kernel through 5.11.3. drivers/scsi/scsi_transport_iscsi.c is adversely affected by the ability of an unprivileged user to craft Netlink messages.