Cybersecurity researchers have discovered what they said is the first known malicious Microsoft Outlook add-in detected in the wild.

In this unusual supply chain attack detailed by Koi Security, an unknown attacker claimed the domain associated with a now-abandoned legitimate add-in to serve a fake Microsoft login page, stealing over 4,000 credentials in the process. The activity has been codenamed AgreeToSteal by the cybersecurity company.

The Outlook add-in in question is AgreeTo, which is advertised by its developer as a way for users to connect different calendars in a single place and share their availability through email. The add-in was last updated in December 2022.

Researchers uncover SSHStalker, an IRC botnet exploiting legacy Linux flaws and SSH servers to build persistent covert access.

A member of the Crazy ransomware gang is abusing legitimate employee monitoring software and the SimpleHelp remote support tool to maintain persistence in corporate networks, evade detection, and prepare for ransomware deployment.

The breaches were observed by researchers at Huntress, who investigated multiple incidents where threat actors deployed Net Monitor for Employees Professional alongside SimpleHelp for remote access to a breached network, while blending in with normal administrative activity.

In one intrusion, attackers installed Net Monitor for Employees Professional using the Windows Installer utility, msiexec.exe, allowing them to deploy the monitoring agent on compromised systems directly from the developer’s site.

The AgreeTo add-in for Outlook has been hijacked and turned into a phishing kit that stole more than 4,000 Microsoft account credentials.

Originally a legitimate meeting scheduling tool for Outlook users, the module was developed by an independent publisher and has been on the Microsoft Office Add-in Store since December 2022.

Office add-ins are just URLs pointing to content loaded into Microsoft products from the developer’s server. In the case of AgreeTo, the developer used a Vercel-hosted URL (outlook-one.vercel.app) but abandoned the project, despite the userbase it formed.

Researchers uncover Reynolds ransomware embedding a vulnerable BYOVD driver to kill EDR defenses, signaling advanced evasion in ransomware attacks.

The fact that the attackers are pursuing the former method is an indication that it likely allows the malicious activity to blend in with typical administrative workflows, helping them avoid detection.

“By abusing legitimate features (password resets and drive mounting) instead of relying solely on a single ‘noisy’ exploit primitive, operators may reduce the effectiveness of detections tuned specifically for known RCE patterns,” Feminella added. “This pace of weaponization is consistent with ransomware operators rapidly analyzing vendor fixes and developing working tradecraft shortly after release.”

When reached for comment about the Warlock ransomware activity targeting SmarterTools, ReliaQuest told The Hacker News that it observed the attackers exploiting CVE-2026–23760 on unpatched systems running versions prior to Build 9,511 shortly after the patch was released.