Microsoft Exchange Server flaw lets attackers misconfigure mailboxes

Microsoft has patched the ProxyToken vulnerability before any evidence of exploitation has emerged

A now-patched vulnerability in Microsoft Exchange Server, dubbed ProxyToken, could be abused by an unauthenticated attacker to perform configuration actions on targeted mailboxes.

This latest flaw in the beleaguered platform is tracked as CVE-2021-33766 and is rated 7.3 out of ten on the threat severity scale, and might give rise to the disclosure of personal information if abused.

A hypothetical example of exploitation, according to researchers with the Zero Day Initiative, could lead to an attacker copying all email addresses on a targeted account and forwarding them to an account controlled by the attacker.  

The flaw lies in the Delegated Authentication feature, a mechanism in which the front-end site passes authentication requests to the back-end system when it detects the presence of a SecurityToken cookie.

Because Microsoft Exchange needs to be specifically configured to use the feature and have the backend carry out checks, the module that handles this delegation isn’t loaded under a default configuration. 

This leads to a bypass as the back-end fails to authenticate incoming requests based on the SecurityToken cookie. The back-end will be completely unaware that it needs to authenticate incoming requests, which means requests can sail through without being subject to authentication on either the front or back-end systems.

Related Resource

2021 state of email security report: Ransomware on the rise

Securing the enterprise in the COVID world

2021 state of email security report: Ransomware on the rise - whitepaper from MimecastFree download

Microsoft patched this vulnerability as part of its Patch Tuesday round of fixes for July, with no evidence so far that hackers have exploited it.

Businesses will be put on high alert in light of the existence of another Microsoft Exchange Server flaw, however, following the supply-chain attack earlier in the year. 

Hackers linked with the Chinese state exploited four flaws in the platform to launch a series of attacks against potentially hundreds of thousands of victims in March, according to security researchers.

The incident was one of many similar supply-chain attacks during 2021, including the infamous SolarWinds hack towards the end of last year.

Featured Resources

The ultimate law enforcement agency guide to going mobile

Best practices for implementing a mobile device program

Free download

The business value of Red Hat OpenShift

Platform cost savings, ROI, and the challenges and opportunities of Red Hat OpenShift

Free download

Managing security and risk across the IT supply chain: A practical approach

Best practices for IT supply chain security

Free download

Digital remote monitoring and dispatch services’ impact on edge computing and data centres

Seven trends redefining remote monitoring and field service dispatch service requirements

Free download

Recommended

Microsoft to shutdown LinkedIn in China
Careers & training

Microsoft to shutdown LinkedIn in China

15 Oct 2021
The future of productivity
Whitepaper

The future of productivity

13 Oct 2021
Microsoft fixes bug preventing Azure Virtual Desktop security updates
Microsoft Azure

Microsoft fixes bug preventing Azure Virtual Desktop security updates

8 Oct 2021
Microsoft backs right to repair following investor revolt
Hardware

Microsoft backs right to repair following investor revolt

8 Oct 2021

Most Popular

Best Linux distros 2021
operating systems

Best Linux distros 2021

11 Oct 2021
HPE wins networking contract with Birmingham 2022 Commonwealth Games
Network & Internet

HPE wins networking contract with Birmingham 2022 Commonwealth Games

15 Oct 2021
Veritas Backup Exec 21.3 review: Covers every angle
backup software

Veritas Backup Exec 21.3 review: Covers every angle

14 Oct 2021