Cybersecurity researchers have reported the first known malicious add-in for Microsoft Outlook, which has been active in the wild. This incident, detailed by Koi Security, involves an attacker taking control of a domain linked to a previously legitimate add-in, leading to the theft of over 4,000 Microsoft credentials.
Details of the Attack
The add-in in question is called AgreeTo, designed to help users consolidate calendars and share availability via email. It was last updated in December 2022. The attack, dubbed AgreeToSteal, exploits a gap in the supply chain, where the original developer abandoned the add-in, allowing the attacker to claim the domain and host a fake Microsoft login page.
Mechanism of Exploitation
According to Idan Dardikman, co-founder and CTO of Koi, this incident highlights a new vector for supply chain attacks. The malicious add-in operates within Outlook, where it can request permissions to read and modify emails. The attacker used the abandoned domain to serve a phishing kit, capturing user credentials and exfiltrating them via the Telegram Bot API.
Potential Risks and Concerns
While the immediate threat involved credential theft, the add-in’s permissions included “ReadWriteItem,” which could allow a malicious actor to deploy JavaScript to siphon email contents covertly. This raises serious concerns about the security of Office add-ins, which are distributed through Microsoft’s store and carry a level of implicit trust.
Recommendations for Improvement
Koi Security has suggested several measures for Microsoft to enhance security, including:
- Triggering a re-review when an add-in’s URL changes content.
- Verifying domain ownership to ensure it remains under the developer’s control.
- Implementing mechanisms to flag or delist outdated add-ins.
- Displaying installation counts to assess impact.
This incident underscores the need for ongoing monitoring of add-ins post-approval, as the current system allows for significant security risks once an add-in is published.
This article was produced by NeonPulse.today using human and AI-assisted editorial processes, based on publicly available information. Content may be edited for clarity and style.
