MITRE ATT&CK · T1539

Steal Web Session Cookie

MITRE · cited in 42 of our lessons

What attackers do. Attackers steal session cookies from browsers or intercept them in transit, then replay them to access web applications and cloud services as the victim. Because the session is already authenticated, this can bypass passwords and MFA. It serves the Credential Access tactic.

How to defend. Shorten session lifetimes for sensitive applications, bind sessions to devices where the platform supports it, and require re-authentication for high-risk actions. Protect endpoints against infostealer malware and adversary-in-the-middle phishing kits, and prefer phishing-resistant MFA. Identity provider and application logs should record session origin details so reuse can be spotted.

Signs to look for. Look for the same session used from a new IP address, country or device shortly after a legitimate login, and processes reading browser cookie stores that are not the browser itself. A common gap is treating a valid session token as proof of the user, without checking context.

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The official text

An adversary may steal web application or service session cookies and use them to gain access to web applications or Internet services as an authenticated user without needing credentials. Web applications and services often use session cookies as an authentication token after a user has authenticated to a website. Cookies are often valid for an extended period of time, even if the web application is not actively used. Cookies can be found on disk, in the process memory of the browser, and in network traffic to remote systems. Additionally, other applications on the targets machine might store sensitive authentication cookies in memory (e.g. apps which authenticate to cloud services). Session cookies can be used to bypasses some multi-factor authentication protocols. There are several examples of malware targeting cookies from web browsers on the local system. Adversaries may also steal cookies by injecting malicious JavaScript content into websites or relying on User Execution by tricking victims into running malicious JavaScript in their browser.

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Lessons that cite it

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