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

Zoomed-in view of the Microsoft Teams logo as seen on the display of a smartphone

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

Managing security risk and compliance in a challenging landscape

How key technology partners grow with your organisation

Download now

Evaluate your order-to-cash process

15 recommended metrics to benchmark your O2C operations

Download now

AI 360: Hold, fold, or double down?

How AI can benefit your business

Download now

Getting started with Azure Red Hat OpenShift

A developer’s guide to improving application building and deployment capabilities

Download now

Recommended

Microsoft Surface Duo review: Progress is a double-edged sword
Mobile Phones

Microsoft Surface Duo review: Progress is a double-edged sword

20 Jan 2021
Best MDM solutions 2020
mobile device management (MDM)

Best MDM solutions 2020

20 Jan 2021
SolarWinds hackers hit Malwarebytes through Microsoft exploit
hacking

SolarWinds hackers hit Malwarebytes through Microsoft exploit

20 Jan 2021
How LogPoint uses MITRE ATT&CK
Whitepaper

How LogPoint uses MITRE ATT&CK

15 Jan 2021

Most Popular

IT retailer faces €10.4m GDPR fine for employee surveillance
General Data Protection Regulation (GDPR)

IT retailer faces €10.4m GDPR fine for employee surveillance

18 Jan 2021
Citrix buys Slack competitor Wrike in record $2.25bn deal
collaboration

Citrix buys Slack competitor Wrike in record $2.25bn deal

19 Jan 2021
Should IT departments call time on WhatsApp?
communications

Should IT departments call time on WhatsApp?

15 Jan 2021