Attacks/Breaches

5/13/2008
05:18 PM
Connect Directly
Google+
LinkedIn
Twitter
RSS
E-Mail
50%
50%

Brute-Force SSH Server Attacks Surge

If such an attack succeeds, the attacker may be able to view, copy, or delete important files on the accessed server or execute malicious code.

The number of brute-force SSH attacks is rising, the SANS Internet Storm Center warned on Monday.

There "has been a significant amount of brute force scanning reported by some of our readers and on other mailing lists," said Internet Storm Center handler Scott Fendley in a blog post. "... From the most recent reports I have seen, the attackers have been using either 'low and slow' style attacks to avoid locking out accounts and/or being detected by IDS/IPS systems. Some attackers seem to be using botnets to do a distributed-style attack, which also is not likely to exceed thresholds common on the network."

Data gathered by DenyHosts.org, a site that tracks SSH hacking attempts, appears to confirm Fendley's claim. A graph of the site's data shows SSH hacking attempts rising sharply over the past weekend.

SSH stands for secure shell. It is a network protocol for creating a secure communications channel between two computers using public key cryptography.

A brute-force SSH attack, a kind of dictionary attack, is simply a repeating, typically automated, attempt to guess SSH client user names and/or passwords. If such an attack succeeds, the attacker may be able to view, copy, or delete important files on the accessed server or execute malicious code.

The SANS Institute last year said that brute-force password-guessing attacks against SSH, FTP, and Telnet servers were "the most common form of attack to compromise servers facing the Internet."

A paper published earlier this year by Jim Owens and Jeanna Matthews of Clarkson University, "A Study of Passwords and Methods Used in Brute-Force SSH Attacks," found, based on an analysis of network traffic, that even "strong" passwords may not be enough to foil password-guessing attacks. ("Strong" passwords are typically a combination of letters and numbers, both upper and lower case, that don't form recognizable words.)

The paper focuses on the vulnerability of Linux systems to brute-force SSH attacks. "While it is true that computers running Linux are not subject to the many worms, viruses, and other malware that target Windows platforms, the Linux platform is known to be vulnerable to other forms of exploitation," the paper states. "A 2004 study conducted by the London-based security analysis and consulting firm mi2g found that Linux systems accounted for 65% of 'digital breaches' recorded during the 12-month period ending in October 2004."

The paper points to remarks by Dave Cullinane, CISO at eBay, and Alfred Huger, VP at Symantec Security Response, to the effect that Linux machines make up a large portion of the command and control networks of botnets.

It also notes that "Linux systems face a unique threat of compromise from brute-force attacks against SSH servers that may be running without the knowledge of system owners/operators. Many Linux distributions install the SSH service by default, some without the benefit of an effective firewall."

Thus, all it takes to compromise such systems is to guess the password, and attackers have machines trying to do just that at all hours of the day. To make matters worse, attackers are sharing dictionaries of username/password pairs that include a significant number of "strong" passwords.

Fendley recommends that IT administrators consider defenses advocated by Owens and Matthews in their paper. These include: using host-based security tools to block access to servers; disabling direct access to root accounts; avoiding easily guessed usernames, such as a person's first or last name; enforcing the use of strong passwords, public key authentication, or multifactor authentication, depending on the security posture of the organization in question; and limiting publicly accessible network services through iptables or other host-based security measures.

Comment  | 
Print  | 
More Insights
Comments
Threaded  |  Newest First  |  Oldest First
5 Reasons the Cybersecurity Labor Shortfall Won't End Soon
Steve Morgan, Founder & CEO, Cybersecurity Ventures,  12/11/2017
Oracle Product Rollout Underscores Need for Trust in the Cloud
Kelly Sheridan, Associate Editor, Dark Reading,  12/11/2017
Register for Dark Reading Newsletters
White Papers
Video
Cartoon Contest
Write a Caption, Win a Starbucks Card! Click Here
Latest Comment: Gee, these virtual reality goggles work great!!! 
Current Issue
The Year in Security: 2017
A look at the biggest news stories (so far) of 2017 that shaped the cybersecurity landscape -- from Russian hacking, ransomware's coming-out party, and voting machine vulnerabilities to the massive data breach of credit-monitoring firm Equifax.
Flash Poll
The State of Ransomware
The State of Ransomware
Ransomware has become one of the most prevalent new cybersecurity threats faced by today's enterprises. This new report from Dark Reading includes feedback from IT and IT security professionals about their organization's ransomware experiences, defense plans, and malware challenges. Find out what they had to say!
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.