InfoSecBulletin Cybersecurity for mankind
A new tool is available on GitHub that gives attackers a way to leverage a recently disclosed vulnerability in Microsoft Teams and automatically deliver malicious files to targeted Teams users in an organization.
The tool, dubbed “TeamsPhisher,” works in environments where an organization allows communications between its internal Teams users and external Teams users — or tenants. It allows attackers to deliver payloads directly into a victim’s inbox without relying on a traditional phishing or social engineering scams to get it there.
Nearly 100,000 email addresses exposed in first AI-related data breach in Singapore
Hackers Exploit Zimbra Mail Servers: TeamViewer patched 5 critical flaws
Google Warns of Hackers Actively Exploiting Citrix 0-Day Flaws
CISA Warns Critical MikroTik RouterOS Flaw While Cisco SD-WAN Zero-Day Exploited in Attacks
Apple Zero-Day Exploited: Pentagon Data Breach Reportedly Exposes Sensitive Data of 3 Million People
JadePuffer Agentic AI targets and destroys Azure’s cloud resources
“InfoSecCon-2026: Bangladesh’s Cybersecurity Leaders Unite to Shape a Safer Digital Future”
Microsoft Patches CVSS 10.0 Azure AI Foundry Vulnerability Allowing Privilege Escalation
AWS is unable to restore access to Bahrain, one UAE cloud data zone after war damage
Cisco Warns of Critical ISE 0-Day Flaw and Hackers Allegedly Selling Fortinet FortiGate 1-Day Flaw
“Give TeamsPhisher an attachment, a message, and a list of target Teams users,” said the tool’s developer Alex Reid, a member of the US Navy’s Red Team, in a description of the tool on GitHub. “It will upload the attachment to the sender’s Sharepoint and then iterate through the list of targets.”
ALSO READ:
A member of the U.S. Navy’s red team has published the tool called TeamsPhisher that exploits a security issue in Microsoft Teams to bypass restrictions on incoming files from external tenants.
The tool works by tricking the client-side protections of Microsoft Teams into treating an external user as an internal one. This is possible because the application has a bug that allows the ID in the POST request of a message to be changed.
The tool was developed by Max Corbridge and Tom Ellson of UK-based security services company Jumpsec, who highlighted the problem last month. They explained that an attacker could use this bug to easily deliver malware to users in a targeted organization.
A Microsoft spokesperson has sent the following comment to media:
‘We’re aware of this report and have determined that it relies on social engineering to be successful. We encourage customers to practice good computing habits online, including exercising caution when clicking on links to web pages, opening unknown files, or accepting file transfers’.
According to GitHub, TeamsPhisher is a Python3 program that facilitates the delivery of phishing messages and attachments to Microsoft Teams users whose organizations allow external communications.
It is not ordinarily possible to send files to Teams users outside one’s organization. Max Corbridge (@CorbridgeMax) and Tom Ellson (@tde_sec) over at JUMPSEC recently disclosed a way to get around this restriction by manipulating Teams web requests in order to alter the recipient of a message with an attached file.
TeamsPhisher incorporates this technique in addition to some earlier ones disclosed by Andrea Santese (@Medu554). It also heavily leans upon TeamsEnum, a fantastic piece of work from Bastian Kanbach (@bka) of SSE, for the authentication part of the attack flow as well as some general helper functions.
