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 newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.

Tags redditAccess control and authenticationExploits / vulnerabilities

Featured

Slideshows

Reseller News launches alumnae breakfast for Women in ICT Awards

Reseller News launches alumnae breakfast for Women in ICT Awards

Reseller News hosted the first alumnae breakfast for the Women in ICT Awards in New Zealand, designed to showcase the leading female leaders in the industry. Held at The Cordis in Auckland, attendees came together to hear inspiring keynotes and panel discussions, alongside high-level networking among peers.

Reseller News launches alumnae breakfast for Women in ICT Awards
Reseller News Innovation Awards 2018: meet the top performing partners

Reseller News Innovation Awards 2018: meet the top performing partners

Reseller News honoured the industry’s finest on a standout evening for the New Zealand channel, recognising the achievements of established partners, emerging players and innovative start-ups, in front of over 460 technology leaders in Auckland.

Reseller News Innovation Awards 2018: meet the top performing partners
Show Comments