Menu
Bug exposes OpenSSH servers to brute-force password guessing attacks

Bug exposes OpenSSH servers to brute-force password guessing attacks

The keyboard-interactive authentication setting could allow for thousands of password retries, a researcher found

Digital key

Digital key

A bug in OpenSSH, the most popular software for secure remote access to UNIX-based systems, could allow attackers to bypass authentication retry restrictions and execute many password guesses.

A security researcher who uses the online alias Kingcope disclosed the issue on his blog last week, but he only requested a public vulnerability ID to be assigned Tuesday.

By default, OpenSSH servers allow six authentication retries before closing a connection and the OpenSSH client allows three incorrect password entries, Kingcope said.

However, OpenSSH servers with keyboard-interactive authentication enabled, which is the default setting on many systems, including FreeBSD ones, can be tricked to allow many authentication retries over a single connection, according to the researcher.

"With this vulnerability an attacker is able to request as many password prompts limited by the 'login grace time' setting, that is set to two minutes by default," Kincope said.

Depending on the server and the connection, two minutes could allow for thousands of retries, which could be enough to guess common or weak passwords using dictionary-based attacks.

According to a discussion on Reddit, setting PasswordAuthentication to 'no' in the OpenSSH configuration and using public-key authentication does not prevent this attack, because keyboard-interactive authentication is a different subsystem that also relies on passwords.

Therefore, users should set ChallengeResponseAuthentication and KbdInteractiveAuthentication to 'no' in their configurations.

Follow Us

Join the New Zealand Reseller News newsletter!

Error: Please check your email address.

Tags redditsecurityAccess control and authenticationExploits / vulnerabilities

Slideshows

Top 50 defining moments of the New Zealand channel in 2016

Top 50 defining moments of the New Zealand channel in 2016

Reseller News looks back on a tumultuous 12 months for the New Zealand channel, assessing the fallout from a year of sizeable industry change. Whether it be local or global mergers and acquisitions, distribution deals or job changes, the channel that started the year differs somewhat to the one set to finish it - Reseller News assesses the key moments that made 2016.​

Top 50 defining moments of the New Zealand channel in 2016
​Hewlett Packard Enterprise honours high achieving NZ channel

​Hewlett Packard Enterprise honours high achieving NZ channel

Hewlett Packard Enterprise honoured its top performing Kiwi partners at the second running of its HPE Partner Awards in New Zealand, held at a glitzy ceremony in Auckland. Recognising excellence across eight categories - from distributors to resellers - the tech giant celebrated its first year as a standalone company, following its official split from HP in 2015.

​Hewlett Packard Enterprise honours high achieving NZ channel
Nutanix treats channel partners to Christmas cruise

Nutanix treats channel partners to Christmas cruise

Nutanix recently took to the seas for a Christmas Cruise around Sydney Harbour with its Australia and New Zealand staff, customers and partners to celebrate a stellar year for the vendor. With the sun out, they were all smiles and mingled over drinks and food.

Nutanix treats channel partners to Christmas cruise
Show Comments