GnuTLS bug exposes Linux clients to server attacks

The maintainers of GnuTLS, a secure communications library used in Red Hat, Ubuntu other Linux distributions, have released fixes for a critical bug affecting the client-side of the software.

The newly discovered vulnerability could allow a malicious server to execute code at its discretion on a requesting client, GnuTLS maintainers said in advisory published on Saturday.

“This vulnerability affects the client side of the gnutls library. A server that sends a specially crafted ServerHello could corrupt the memory of a requesting client,” the developers noted.

The GnuTLS library implements the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols, offering numerous Linux distributions and applications the tools to access secure communications. So while GnuTLS offers privacy over insecure channels, the bug means it’s possible for an attacker to crash or take control of a PC when it’s attempting to establish a secure connection with the attacker’s server.

GnuTLS chief developer and Red Hat engineer Nikos Mavrogiannopoulos released updates for the library on Saturday in the form of GnuTLS versions 3.1.25, 3.2.15, and 3.3.3.

A more comprehensive write-up on the bug by Red Hat, which rated the bug’s priority as “high severity”, indicates the flaw stems from an insufficient session_id check during the TLS/SSL handshake.

“A flaw was found in the way GnuTLS parsed session ids from Server Hello packets of the TLS/SSL handshake. A malicious server could use this flaw to send an excessively long session id value and trigger a buffer overflow in a connecting TLS/SSL client using GnuTLS, causing it to crash or, possibly, execute arbitrary code,” the company wrote.

“The flaw is in read_server_hello() / _gnutls_read_server_hello(), where session_id_len is checked to not exceed incoming packet size, but not checked to ensure it does not exceed maximum session id length.”

According to Red Hat, the bug affects all versions of Fedora and Extra Packages for Enterprise Linux (EPEL) version 5.

The flaw was initially reported by Joonas Kuorilehto of Codenomicon — the company responsible for discovering the recent OpenSSL Heartbleed bug.

The latest bug affecting Linux distributions through GnuTLS doesn’t appear to be as serious as the flaw Red Hat’s security team discovered earlier this year during an audit. While Red Hat gives them equivalent priority ratings, the earlier flaw could have allowed an attacker to dupe GnuTLS to accept a fake certificate as valid, making it possible for an attacker to monitor traffic in plain text and inject arbitrary code.

Follow @CSO_Australia and sign up to the CSO Australia newsletter.

This article is brought to you by Enex TestLab, content directors for CSO Australia.

Join the CSO newsletter!

Error: Please check your email address.

Tags LinuxGnuTLS

More about CSOEnex TestLabFedoraLinuxRed HatUbuntu

Show Comments

Featured Whitepapers

Editor's Recommendations

Solution Centres

Stories by Liam Tung

Latest Videos

  • 150x50

    CSO Webinar: Will your data protection strategy be enough when disaster strikes?

    Speakers: - Paul O’Connor, Engagement leader - Performance Audit Group, Victorian Auditor-General’s Office (VAGO) - Nigel Phair, Managing Director, Centre for Internet Safety - Joshua Stenhouse, Technical Evangelist, Zerto - Anthony Caruana, CSO MC & Moderator

    Play Video

  • 150x50

    CSO Webinar: The Human Factor - Your people are your biggest security weakness

    ​Speakers: David Lacey, Researcher and former CISO Royal Mail David Turner - Global Risk Management Expert Mark Guntrip - Group Manager, Email Protection, Proofpoint

    Play Video

  • 150x50

    CSO Webinar: Current ransomware defences are failing – but machine learning can drive a more proactive solution

    Speakers • Ty Miller, Director, Threat Intelligence • Mark Gregory, Leader, Network Engineering Research Group, RMIT • Jeff Lanza, Retired FBI Agent (USA) • Andy Solterbeck, VP Asia Pacific, Cylance • David Braue, CSO MC/Moderator What to expect: ​Hear from industry experts on the local and global ransomware threat landscape. Explore a new approach to dealing with ransomware using machine-learning techniques and by thinking about the problem in a fundamentally different way. Apply techniques for gathering insight into ransomware behaviour and find out what elements must go into a truly effective ransomware defence. Get a first-hand look at how ransomware actually works in practice, and how machine-learning techniques can pick up on its activities long before your employees do.

    Play Video

  • 150x50

    CSO Webinar: Get real about metadata to avoid a false sense of security

    Speakers: • Anthony Caruana – CSO MC and moderator • Ian Farquhar, Worldwide Virtual Security Team Lead, Gigamon • John Lindsay, Former CTO, iiNet • Skeeve Stevens, Futurist, Future Sumo • David Vaile - Vice chair of APF, Co-Convenor of the Cyberspace Law And Policy Community, UNSW Law Faculty This webinar covers: - A 101 on metadata - what it is and how to use it - Insight into a typical attack, what happens and what we would find when looking into the metadata - How to collect metadata, use this to detect attacks and get greater insight into how you can use this to protect your organisation - Learn how much raw data and metadata to retain and how long for - Get a reality check on how you're using your metadata and if this is enough to secure your organisation

    Play Video

  • 150x50

    CSO Webinar: How banking trojans work and how you can stop them

    CSO Webinar: How banking trojans work and how you can stop them Featuring: • John Baird, Director of Global Technology Production, Deutsche Bank • Samantha Macleod, GM Cyber Security, ME Bank • Sherrod DeGrippo, Director of Emerging Threats, Proofpoint (USA)

    Play Video

More videos

Blog Posts

Market Place