Multi-Factor Authentication (MFA) is one of the most effective defenses against account takeover attacks, but cybercriminals are constantly evolving their methods to bypass it. One of the latest threats targeting Office 365 users involves cookie theft, allowing attackers to gain unauthorized access even when MFA is enabled.
What Is Cookie Theft?
Cookie theft, also known as session hijacking, is an attack where cybercriminals steal authentication cookies from a user’s browser. These cookies store session information, keeping users logged in without requiring them to enter credentials repeatedly. If an attacker gains access to these cookies, they can impersonate the user without needing their password or MFA verification.
How Attackers Are Targeting Office 365
Cybercriminals use a combination of phishing, malware, and adversary-in-the-middle (AiTM) attacks to steal cookies from Office 365 users. Here’s how it typically happens:
- Phishing Attacks – Attackers send convincing phishing emails impersonating Microsoft or an IT administrator, tricking users into visiting a fake login page.
- AiTM Attack – The phishing site acts as a middleman, capturing authentication cookies as users log in to their real Office 365 accounts.
- Session Hijacking – Once the attacker has stolen the session cookie, they inject it into their browser, bypassing MFA and gaining full access to the Office 365 account.
- Business Email Compromise (BEC) – Attackers often use the hijacked account to send fraudulent emails, launch further phishing attacks, or execute financial fraud.
Why This Attack Is Dangerous
- MFA Bypass – Since attackers use stolen session cookies, they don’t need to go through MFA verification.
- Stealthy Access – Many security tools don’t detect session hijacking since no new login attempt occurs.
- Persistent Threats – Attackers can maintain access as long as the stolen session remains valid, potentially for days or weeks.
What Can We Do To Protect Our Account?
1. Regularly Clear Cookies and Sessions
Encouraging users to log out regularly and clear browser cookies can reduce the risk of persistent session hijacking. Organizations should implement policies that require users to sign out of accounts when not in use and automatically log users out after a certain period of inactivity. Additionally, IT teams can enforce browser settings that periodically clear cookies, preventing long-term session storage. Using secure browsers with built-in security features can also help mitigate risks.
2. Educate Users on Phishing Threats
Training employees to recognize phishing emails, verify URLs, and report suspicious activity is crucial in preventing credential theft. Regular phishing simulation exercises can help users develop a keen eye for fraudulent emails. Organizations should also provide training on how to use security tools, such as email filtering and web security solutions, to further reduce the likelihood of falling for phishing scams. Encouraging a culture of cybersecurity awareness ensures that employees remain vigilant against evolving threats.
Final Thoughts
Cookie theft is a sophisticated attack method that allows cybercriminals to bypass MFA and infiltrate Office 365 accounts. Organizations must stay ahead by implementing robust security measures, monitoring for suspicious activity, and educating users about emerging threats.
By taking a proactive approach, businesses can significantly reduce the risk of falling victim to these evolving cyber threats. If your business needs assistance, feel free to call SandStorm IT at 901-475-0275.