Researchers find bug allowing hackers to bypass first factor authentication of users accounts

Found by Duo security in a third-party library in its own authentication gateway

Researchers uncovered a bug that could have allowed cyber crooks to bypass the first authentication step of user accounts protected by single sign-on (SSO).

Found by security company Duo, the firm discovered the implementation flaw in a third-party library in its own authentication gateway, Duo Network Gateway (DNG), late last year. After giving vendors time to fix the bug, it disclosed the problem responsibly. It's only now that the details of how worryingly effective the bug is have gone public.

Located in the open-source library 'python-saml' (CVE-2017-11427), the firm's researchers said that under certain configurations, the flaw could have allowed an attacker with authenticated access to a SAML Identity Provider (IdP) to bypass the first factor of authentication for a different user.

After a bit of digging, it was revealed that the flaw was reflected in many other SSO applications, thanks to a problem in handling the underlying "authentication language", something which has become a standard for products in this space.

"This issue is due to an inconsistency of XML DOM traversal APIs and their handling of comment nodes," Duo explained in a blog post. "Comment nodes should have no effect - and indeed, due to the canonicalisation of XML prior to signature verification, inserting an XML comment into a SAML message does not invalidate its signature."

However, the firm said the 'python-saml' code makes incorrect use of a DOM-traversal API, such that it fails to extract the full inner text of an XML element containing a comment. Instead, all the text after the comment is lost.

"To exploit this issue, an attacker inserts XML comments into select areas of the SAML assertions before passing them along to the DNG," the firm continued. "Once the DNG validates the signature and extracts the user's identifier, only part of the user's identifier is recovered."

Duo said that in cases where an attacker's user identifier (for example: john_doe) can be truncated to become a victim's user identifier (for example: john), the attacker can trick the DNG into authenticating as the victim.

Luckily, however, the issue has been resolved now through a patch to the Duo Network Gateway, and its public announcement has allowed other security firms to fix potentially similar issues in their authentication gateways.

Main image credit: Shutterstock 

Featured Resources

Navigating the new normal: A fast guide to remote working

A smooth transition will support operations for years to come

Download now

Leading the data race

The trends driving the future of data science

Download now

How to create 1:1 customer experiences at scale

Meet the technology capable of delivering the personalisation your customers crave

Download now

How to achieve daily SAP releases

Accelerate the pace of SAP change to support your digital strategy

Download now

Recommended

8 most secure web browsers
web browser

8 most secure web browsers

25 Sep 2020
Your essential guide to internet security
Security

Your essential guide to internet security

23 Sep 2020
How to enable private browsing on any device
privacy

How to enable private browsing on any device

22 Sep 2020
Third-party apps are tracking your WhatsApp activity
social media

Third-party apps are tracking your WhatsApp activity

21 Sep 2020

Most Popular

Microsoft hints at stand-alone successor to Office 2019 suite
Microsoft Office

Microsoft hints at stand-alone successor to Office 2019 suite

24 Sep 2020
16 ways to speed up your laptop
Laptops

16 ways to speed up your laptop

16 Sep 2020
16 ways to speed up your laptop
Laptops

16 ways to speed up your laptop

16 Sep 2020