• Home
  • Cyber Crime
  • Cyber warfare
  • APT
  • Data Breach
  • Deep Web
  • Digital ID
  • Hacking
  • Hacktivism
  • Intelligence
  • Internet of Things
  • Laws and regulations
  • Malware
  • Mobile
  • Reports
  • Security
  • Social Networks
  • Terrorism
  • ICS-SCADA
  • POLICIES
  • Contact me
MUST READ

U.S. CISA adds Cisco ISE and PaperCut NG/MF flaws to its Known Exploited Vulnerabilities catalog

 | 

Critical WordPress Post SMTP plugin flaw exposes 200K+ sites to full takeover

 | 

Scattered Spider targets VMware ESXi in using social engineering

 | 

China-linked group Fire Ant exploits VMware and F5 flaws since early 2025

 | 

Allianz Life data breach exposed the data of most of its 1.4M customers

 | 

SECURITY AFFAIRS MALWARE NEWSLETTER ROUND 55

 | 

Security Affairs newsletter Round 534 by Pierluigi Paganini – INTERNATIONAL EDITION

 | 

Law enforcement operations seized BlackSuit ransomware gang’s darknet sites

 | 

Arizona woman sentenced for aiding North Korea in U.S. IT job fraud scheme

 | 

Operation CargoTalon targets Russia’s aerospace with EAGLET malware,

 | 

Unpatched flaw in EoL LG LNV5110R cameras lets hackers gain Admin access

 | 

Koske, a new AI-Generated Linux malware appears in the threat landscape

 | 

Mitel patches critical MiVoice MX-ONE Auth bypass flaw

 | 

Coyote malware is first-ever malware abusing Windows UI Automation

 | 

SonicWall fixed critical flaw in SMA 100 devices exploited in Overstep malware attacks

 | 

DSPM & AI Are Booming: $17.87B and $4.8T Markets by 2033

 | 

Stealth backdoor found in WordPress mu-Plugins folder

 | 

U.S. CISA adds CrushFTP, Google Chromium, and SysAid flaws to its Known Exploited Vulnerabilities catalog

 | 

U.S. CISA urges FCEB agencies to fix two Microsoft SharePoint flaws immediately and added them to its Known Exploited Vulnerabilities catalog

 | 

Sophos fixed two critical Sophos Firewall vulnerabilities

 | 
  • Home
  • Cyber Crime
  • Cyber warfare
  • APT
  • Data Breach
  • Deep Web
  • Digital ID
  • Hacking
  • Hacktivism
  • Intelligence
  • Internet of Things
  • Laws and regulations
  • Malware
  • Mobile
  • Reports
  • Security
  • Social Networks
  • Terrorism
  • ICS-SCADA
  • POLICIES
  • Contact me
  • Home
  • Breaking News
  • Hacking
  • Microsoft warns of a evasive year-long spear-phishing campaign targeting Office 365 users

Microsoft warns of a evasive year-long spear-phishing campaign targeting Office 365 users

Pierluigi Paganini August 13, 2021

Microsoft warns of a long-running spear-phishing campaign that has targeted Office 365 customers in multiple attacks since July 2020.

Microsoft revealed that a year-long spear-phishing campaign has targeted Office 365 customers in multiple attacks starting with July 2020.

The attackers used invoice-themed XLS.HTML attachments, Microsoft reported that they changed obfuscation and encryption mechanisms every 37 days on average, a circumstance that demonstrates high motivation and the threat actors’ abilities to constantly evade detection.

“The HTML attachment is divided into several segments, including the JavaScript files used to steal passwords, which are then encoded using various mechanisms. These attackers moved from using plaintext HTML code to employing multiple encoding techniques, including old and unusual encryption methods like Morse code, to hide these attack segments.” reads the report published by the Microsoft 365 Defender Threat Intelligence Team. “Some of these code segments are not even present in the attachment itself. Instead, they reside in various open directories and are called by encoded scripts.”

Attackers split the HTML attachment in individual segments that appear harmless and bypass security solutions.

Experts believe the attackers aims at harvesting usernames, passwords, and recent waves of attacks, other information such as IP address and location, that could be used in later attacks. 

These attacks are very effective because of efforts to obfuscate their phishing emails to bypass email security solutions.

“In the case of this phishing campaign, these attempts include using multilayer obfuscation and encryption mechanisms for known existing file types, such as JavaScript. Multilayer obfuscation in HTML can likewise evade browser security solutions,” contines Microsoft.

The HTML attachment is divided into multiple segments, which are encoded using various encoding mechanisms. 

The segments composing the attachment include:

  • Segment 1 – Email address of the target
  • Segment 2 – Logo of the targeted user’s organization from logo[.]clearbit[.]com, i[.]gyazo[.]com, or api[.]statvoo[.]com; if the logo is not available, this segment loads the Microsoft Office 365 logo instead.
  • Segment 3 – A script that loads an image of a blurred document, indicating that sign-in has supposedly timed out.
  • Segment 4 – A script that prompts the user to enter their password, submits the entered password to a remote phishing kit, and displays a fake page with an error message to the user.

Threat actors used to change the encoding mechanisms to evade detection, they used different methods for each segment and alternate the use of plaintext HTML code, escaping, Base64, ASCII chars, and even Morse code. 

Office 365 Phishing

Upon tricking the recipient into launching the attachment, it will display a fake Office 365 login form over a blurred Excel document. The login dialog box is designed using the logo of the recipient’s organization and in some cases the “username” field is filled with the targets’ email addresses and requests the victim to provide its password to view the Office document.

Office 365 Phishing

If the recipient provides its password, a script will display an alert informing the victim that the password is incorrect and send the password to the attacker.

Microsoft shared Indicators of Compromise (IoCs) for this campaign.

Follow me on Twitter: @securityaffairs and Facebook

[adrotate banner=”9″][adrotate banner=”12″]

Pierluigi Paganini

(SecurityAffairs – hacking, cybercrime)

[adrotate banner=”5″]

[adrotate banner=”13″]


facebook linkedin twitter

Hacking hacking news information security news IT Information Security Office 365 phishing Pierluigi Paganini Security Affairs Security News spear phishing

you might also like

Pierluigi Paganini July 28, 2025
U.S. CISA adds Cisco ISE and PaperCut NG/MF flaws to its Known Exploited Vulnerabilities catalog
Read more
Pierluigi Paganini July 28, 2025
Critical WordPress Post SMTP plugin flaw exposes 200K+ sites to full takeover
Read more

leave a comment

newsletter

Subscribe to my email list and stay
up-to-date!

    recent articles

    U.S. CISA adds Cisco ISE and PaperCut NG/MF flaws to its Known Exploited Vulnerabilities catalog

    Security / July 28, 2025

    Critical WordPress Post SMTP plugin flaw exposes 200K+ sites to full takeover

    Security / July 28, 2025

    Scattered Spider targets VMware ESXi in using social engineering

    Cyber Crime / July 28, 2025

    China-linked group Fire Ant exploits VMware and F5 flaws since early 2025

    Hacking / July 28, 2025

    Allianz Life data breach exposed the data of most of its 1.4M customers

    Data Breach / July 27, 2025

    To contact me write an email to:

    Pierluigi Paganini :
    pierluigi.paganini@securityaffairs.co

    LEARN MORE

    QUICK LINKS

    • Home
    • Cyber Crime
    • Cyber warfare
    • APT
    • Data Breach
    • Deep Web
    • Digital ID
    • Hacking
    • Hacktivism
    • Intelligence
    • Internet of Things
    • Laws and regulations
    • Malware
    • Mobile
    • Reports
    • Security
    • Social Networks
    • Terrorism
    • ICS-SCADA
    • POLICIES
    • Contact me

    Copyright@securityaffairs 2024

    We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept All”, you consent to the use of ALL the cookies. However, you may visit "Cookie Settings" to provide a controlled consent.
    Cookie SettingsAccept All
    Manage consent

    Privacy Overview

    This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities...
    Necessary
    Always Enabled
    Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
    Non-necessary
    Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.
    SAVE & ACCEPT