How Session Cookies Bypass MFA Entirely
(And Why “MFA Enabled” Is No Longer Enough for MSPs)
Many MSPs consider their systems secure once MFA is enabled.
Clients often assume that having MFA in place ensures complete protection.
However, many account takeovers still occur even when MFA is fully enabled. (Wallace, 2025)The cause is session cookies.
Session cookies.
MFA Protects Logins — Not Active Sessions
MFA verifies a user only at the time of sign-in.After a successful login, the system issues a session cookie that indicates:“This user is trusted. Don’t ask again.”If an attacker obtains the session cookie, they do not need:
- A password
- An MFA code
- User interaction
They can simply reuse the session.To the platform, all activity appears legitimate. (Cookie-Bite Attack: How Cybercriminals Steal Browser Sessions, 2025)
Why This Matters to MSPs
At this point, risk shifts from technology failure to provider responsibility.When a breach happens:
- Logs show “successful login.”
- MFA appears satisfied
- No alerts are triggered
Clients then ask the question every MSP dreads:“But you said we were protected.”
How Attackers Steal Session Cookies
Modern attacks are both discreet and rapid. Common entry points include:
- Adversary-in-the-Middle (AiTM) phishing pages
- Malicious browser extensions
- Info-stealer malware
- Personal or unmanaged devices (Seetharam et al., 2025)
After a user signs in, the attacker captures the session token and reuses it.No brute force.
No MFA fatigue.
No failed sign-ins.
What Attackers Do After Access
Session-based access provides attackers with time, which increases potential damage. (Session Hijacking in 2025: Techniques, Attack Examples & Defenses, 2025)Typical actions include:
- Creating hidden inbox rules
- Exfiltrating SharePoint or OneDrive data
- Adding OAuth applications
- Sending internal phishing emails
- Modifying audit or alert settings (Investigate app governance threat detection alerts - Microsoft Defender for Cloud Apps, 2024)
By the time the breach is detected, the attacker has often already left. (Narayanan et al., 2018)
Why “MFA Enabled” Is No Longer a Selling Point
For MSPs, this presents an uncomfortable reality:
MFA is now considered a baseline requirement rather than a comprehensive control. (CISA Mandates Multi-Factor Authentication for All Federal Agencies by Q1 2026, 2025)
Clients expect it.
Insurers expect it.
Attackers: The critical factor is how sessions are managed after MFA authentication.
What MSPs Should Be Enforcing Instead
To reduce risk and liability, MSPs should prioritize session-aware security measures:
- Conditional Access with sign-in frequency limits
- Device compliance enforcement
- Blocking unmanaged or personal devices
- Phishing-resistant MFA (FIDO2 / passkeys)
- Token protection and binding
- Continuous Access Evaluation (CAE)
This approach transforms security from a single login verification to continuous trust evaluation. (Continuous Adaptive Trust: What it is, Benefits, & Key Principles, 2024)
The MSP Risk Nobody Talks About
When session controls are not enforced:
- MFA may provide a false sense of security
- Breaches look “legitimate” in logs
- Incident response becomes harder
- MSP credibility is negatively impacted
Attackers do not bypass MFA directly.
Instead, they circumvent it.
Final Takeaway for MSP Owners
If your security strategy ends with enabling MFA,you are securing initial access but leaving internal systems vulnerable..Session security is now a core service responsibility, not an optional enhancement.
Jaspreet Singh — Author at MSPinsights.ca | Founder & CEO, Accelerate IT Services Inc.
References
Wallace, B. (December 7, 2025). 65% of ATO Victims Had MFA Enabled, But Still Got Hacked: Here’s How. WebProNews. https://www.webpronews.com/mfa-hacked/
(April 14, 2025). Cookie-Bite Attack: How Cybercriminals Steal Browser Sessions. STORM Guidance. https://www.cyber.care/insight/cookie-bite-and-session-hijacking-how-cybercriminals-bypass-passwords
Narayanan, S., Ganesan, A., Joshi, K., Oates, T., Joshi, A. & Finin, T. (2018). Cognitive Techniques for Early Detection of Cybersecurity Events. arXiv preprint arXiv:1808.00116. https://doi.org/10.48550/arXiv.1808.00116
(2025). Session Hijacking in 2025: Techniques, Attack Examples & Defenses. Seraphic Security. https://seraphicsecurity.com/learn/website-security/session-hijacking-in-2025-techniques-attack-examples-and-defenses/
(2024). Investigate app governance threat detection alerts - Microsoft Defender for Cloud Apps. Microsoft Learn. https://learn.microsoft.com/en-us/defender-cloud-apps/app-governance-anomaly-detection-alerts
(2024). Continuous Adaptive Trust: What it is, Benefits, & Key Principles. Syteca. https://www.syteca.com/en/blog/continuous-adaptive-trust
(December 12, 2025). CISA Mandates Multi-Factor Authentication for All Federal Agencies by Q1 2026. CloudStack Networks. https://www.cloudstacknetworks.com/news/cmj4wqt3b0003wbrr3clcty42
Seetharam, S. B., Nabeel, M. & Melicher, W. (2025). Malicious GenAI Chrome Extensions: Unpacking Data Exfiltration and Malicious Behaviours. arXiv preprint arXiv:2512.10029. https://doi.org/10.48550/arXiv.2512.10029