Zero-click 'wormable' RCE flaw uncovered in Microsoft Teams

Researcher complains that Microsoft underscored the significance of the flaw, which could be triggered without user interaction

Hackers were able to exploit a serious vulnerability in Microsoft Teams desktop apps to execute arbitrary code remotely and spread infection across a company network by simply sending a specially-crafted message.

The zero-click flaw, which is wormable, can be triggered by cross-site scripting (XSS) injection in Teams, with hackers able to transmit a malicious message which will execute code without user interaction.

This remote code execution (RCE) flaw was first reported to Microsoft in August, with the company fixing the bugs in October 2020. However, security researcher Oskars Vegaris, who discovered the flaw,  has complained that the firm didn’t take his report as seriously as it should have, with Microsoft not even assigning the bug a CVE tag.

Microsoft considered the Teams vulnerability as ‘important’ although described its impact as ‘spoofing’ in its bug bounty programme. As for the CVE element, Microsoft doesn’t issue CVE tags on products that automatically update without user interaction.

“This report contains a new XSS vector and a novel RCE payload which are used together,” Vegaris wrote on GitHub. “It affects the chatting system within Microsoft Teams and can be used in e.g. direct messages, channels.”

In a technical breakdown of the vulnerability, the researcher highlighted how RCE can be achieved by chaining two flaws, including stored XSS in Teams chat functionality and a cross-platform JavaScript exploit for the Teams desktop client. 

The impact is seemingly alarming, with its wormable nature meaning the exploit payload can be spread across other users, channels and companies without any interaction. The execution of malicious code could also happen without any user interaction, given users need to only view the specially-crafted message. 

The consequences of infection range from complete loss of confidentiality and integrity for victims, to access to private communications, internal networks, private keys as well as personal data outside of Microsoft Teams.

Hackers can also gain access to single sign-on (SSO) tokens for other services, including Microsoft services such as Outlook or Microsoft 365. This will expose them to possible phishing attacks too, as well as keylogging with specially-crafted payloads, according to Vegaris.

“We mitigated the issue with an update in October, which has automatically deployed and protected customers.” A Microsoft spokesperson told IT Pro, adding that no further customer action is necessary. 

Featured Resources

Consumer choice and the payment experience

A software provider's guide to getting, growing, and keeping customers

Download now

Prevent fraud and phishing attacks with DMARC

How to use domain-based message authentication, reporting, and conformance for email security

Download now

Business in the new economy landscape

How we coped with 2020 and looking ahead to a brighter 2021

Download now

How to increase cyber resilience within your organisation

Cyber resilience for dummies

Download now

Recommended

ProtectedBy.AI’s CodeLock blocks malware at source code level
software as a service (SaaS)

ProtectedBy.AI’s CodeLock blocks malware at source code level

9 Jun 2021
CISOs aren’t leading by example when it comes to cyber security
cyber security

CISOs aren’t leading by example when it comes to cyber security

24 May 2021
New report highlights the need for diversity in cyber security recruitment
cyber security

New report highlights the need for diversity in cyber security recruitment

28 Apr 2021
HackBoss malware is using Telegram to steal cryptocurrency from other hackers
cryptocurrencies

HackBoss malware is using Telegram to steal cryptocurrency from other hackers

16 Apr 2021

Most Popular

How to find RAM speed, size and type
Laptops

How to find RAM speed, size and type

16 Jun 2021
What is HTTP error 400 and how do you fix it?
Network & Internet

What is HTTP error 400 and how do you fix it?

16 Jun 2021
EU plans to launch bloc-wide cyber task force
cyber attacks

EU plans to launch bloc-wide cyber task force

22 Jun 2021