If you suspect a browser extension or web session has been compromised, disable or remove the extension, then separately secure the accounts it could access. Removing an extension does not necessarily end existing website sessions or revoke access tokens. If evidence matters—especially at work—record the extension and its permissions before removing it.
What to do first
- Limit or remove the extension. In Chrome, open More > Extensions > Manage extensions. You can turn an extension off, remove it, or restrict its site access to a specific site, all sites, or only when you activate it. See Google Chrome Help: Install and manage extensions. If you need to preserve evidence, record its details before changing it.
- Secure affected accounts from a clean device. Use each service’s security controls to terminate active sessions and revoke tokens or connected-app access. If you suspect a password was exposed, change it from a device you believe is clean, and enable multifactor authentication where available.
- Check for a broader device problem. If browser settings keep changing, pages are being modified, you lose control of the browser, or Chrome reports that a suspicious program is changing extension files, investigate the device as well as the extension. Run reputable antivirus or anti-malware protection and remove suspicious apps or add-ons. Microsoft describes these behaviors in its guidance on unwanted software; Chrome provides advice on resetting Chrome settings to default.
- Review connected applications separately. Check account security settings for unfamiliar apps and OAuth permissions. Removing an extension will not revoke a separate consent grant. For work accounts, administrators should also examine sign-in and audit activity. Microsoft’s guidance on protecting against consent phishing explains how to investigate suspicious app permissions.
How to assess whether an extension is suspicious
No single clue proves an extension is malicious, and a lack of visible symptoms does not prove it is safe. A familiar name, store listing, positive reviews, or normal-looking function is not enough: documented malicious extensions have used AI-related branding and browser-store distribution. Assess the publisher’s identity, requested permissions, version history, behavior, and whether its access makes sense for its stated purpose.
Pay attention to permissions that allow access to browsing activity or page content, especially when that access seems broader than the extension’s purpose. Unexpected redirects, changed search behavior, unfamiliar pop-ups, or altered pages are reasons to investigate, but quiet data collection may not produce an obvious warning.
For example, Microsoft Security reported on March 5, 2026, that a Chrome and Edge extension collected visited URLs and portions of AI chats, stored local identifiers and queued telemetry, and periodically sent data over HTTPS. In a separate report dated June 29, 2026, Microsoft Threat Intelligence described “Search for perplexity ai” (ID flkebkiofojicogddingbdmcmkpbplcd, version 2.2), which routed search queries and typed suggestions through attacker-controlled infrastructure. Microsoft said the extension was taken down after responsible disclosure, while noting that its observed analysis did not definitively confirm credential theft. These are individual documented incidents, not evidence of how common such extensions are or proof that another extension behaves the same way. Read the reports on malicious AI assistant extensions harvesting chat histories and a Chromium extension redirecting browser search.
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Can an extension steal cookies or keep a session open?
Potentially, an extension with access to relevant browser data can expose information that may help an attacker, but the extension’s name or permissions alone do not establish that it stole cookies or credentials. NIST describes browser cookies as the predominant mechanism for creating and tracking sessions and as short-term secrets for a session. It also notes that access and associated refresh tokens can remain valid after an authentication session ends. That is why disabling an extension and signing out of an account are separate steps.
For each potentially affected service, use its security page to sign out other sessions, revoke tokens if that option exists, and remove unfamiliar connected applications. Controls and labels differ by service. NIST’s SP 800-63B session management guidance says: “Sessions SHOULD provide a readily accessible mechanism for subscribers to terminate (i.e., log off) their session when their interaction is complete.”
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What to record before removal
If you need to report the incident, preserve basic details before disabling or removing the extension. Do not delay containment if the risk is immediate; make a quick record if practical, then restrict access.
- Extension name, browser, version, and extension ID if visible.
- Requested permissions and current site-access settings.
- When it was installed or last updated, if known.
- Symptoms, affected websites, and approximate times they occurred.
- Whether the extension was enabled and which user or device was affected.
For a workplace incident, share this information with your IT or security team rather than attempting broad cleanup on your own. Changing or deleting artifacts can make it harder to understand scope.
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Steps for IT teams investigating a managed fleet
Start by determining which users and devices have the extension, whether it is enabled, and which versions and permissions are present. Assess scope before remediation, then apply organizational allow or block decisions. Microsoft Defender Vulnerability Management can assess browser extensions on Windows devices running Edge, Chrome, or Firefox, including extension versions, users, devices, enabled state, requested permissions, and associated permission-risk information. Its documented assessment is Windows-only; details are in Microsoft’s browser extensions assessment documentation.
Permission risk is partly a policy judgment: Microsoft says organizations should set their own risk tolerance. NSA browser guidance recommends considering controls to prevent unauthorized extension installation, removing unnecessary extensions, and using allowlisting where supported. It also discusses browser isolation as an additional defensive layer. The NSA document dates to May 2018, so treat its named product and operating-system examples as historical rather than current feature recommendations. See the NSA Steps to Secure Web Browsing.
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