The Ransomware Attack That Started with an Encrypted ZIP file
March 27, 2026

The Ransomware Attack That Started with an Encrypted ZIP file

A Familiar Email with a Hidden Threat

It begins with an email. The sender appears to be a regular supplier, a name the accounts payable coordinator at a mid-size logistics company recognizes immediately. The message is brief and professional: a new invoice is attached, password-protected for security, with the password provided in the email body. The coordinator processes dozens of vendor invoices each week. This one looks like all the others.

They download the ZIP file, enter the password, extract the contents, and double-click what appears to be a PDF.

Within seconds, a loader executes silently in the background. Over the next several hours, it moves laterally through the network, identifies file shares and backup targets, and begins encrypting. By the time the IT team notices unusual storage activity, three servers and a shared drive containing operational records are locked. A ransom note appears on screen.

Why Password-Protected Files Are a Hidden Risk

The attack did not start with a zero-day vulnerability or a sophisticated intrusion. It started with a PDF inside a password-protected ZIP, delivered through a supplier email address that had been compromised weeks earlier. And it succeeded largely because of a gap that most organizations are not aware of: traditional antivirus tools and endpoint scanners typically skip encrypted archives. Because the contents are protected by a password, the scanner cannot see inside. It marks the file as unreadable and passes it through.

This is not an edge case. Password-protected attachments are increasingly common in legitimate business communication and exploited by attackers for exactly that reason. The feature that makes the delivery mechanism look credible is the same feature that renders it invisible to conventional scanning.

How Chrome Enterprise Premium Blocks the Threat Before It Hits

Chrome Enterprise Premium's deep scanning capability addresses this gap at the browser level which is exactly where the threat enters. When a file is downloaded through Chrome, it is sent to Google's cloud-based scanning infrastructure before it reaches the local endpoint. For password-protected archives where the password is supplied in context, as it was in this scenario, the system can attempt extraction and scan the contents directly. Suspicious payloads are identified and blocked before the file completes its download.

The coordinator never gets the chance to extract and execute the malicious document, because Chrome intercepts the process before it reaches the local filesystem. This matters because the browser is the delivery channel. The attacker did not exploit a server vulnerability or breach a firewall. They sent a file through a web-accessible email client, knowing it would be opened in a browser. Chrome Enterprise Premium treats the browser as the security perimeter; it has become not just a window to the web, but an enforcement point for content that enters the organization.

Comprehensive Coverage for High-Volume Files

Deep scanning also covers large files, a category that endpoint tools frequently deprioritize due to performance constraints. For logistics organizations that regularly receive large manifests, shipping documents, and multi-page PDFs from suppliers, this coverage is not a luxury, it is a necessity. Beyond blocking the immediate threat, Chrome Enterprise Premium logs every download event and scan result, giving the security team visibility into what files employees are retrieving and from which sources. Over time, this telemetry helps identify patterns of suppliers whose domains are generating repeated flags, file types disproportionately associated with risk that can inform broader threat response and supplier vetting processes.

See It in Your Environment First with Chrome Readiness Tool

Ransomware consistently finds its way into the devices that are least monitored and least protected. In the context of malware delivery, domain access behavior is one of the most telling signals available. Rather than applying a fixed external definition of what counts as dangerous, administrators use the Custom Domain Readiness feature to make that call themselves, marking domains as restricted based on internal policy or clearing ones that have been verified as safe. Suppliers whose domains repeatedly generate flags become visible before they become a problem.

Extensions add a second layer of risk. A browser add-on installed outside the official web store, flagged as unverified by the tool, could be intercepting download activity or manipulating page content without the IT team's knowledge. Admins can review extension classifications in the Report Generator and adjust them based on internal security validation. A device is classified as unsecured when restricted domains have been accessed or unverified extensions are present, giving teams a concrete starting point for prioritizing which endpoints need attention first.

Use the Chrome Readiness Tool to understand where your browser-level exposure is concentrated, then use Chrome Enterprise Premium's deep scanning to make sure what comes through the browser does not become the starting point of your next incident.

Blog Editors Team

Chrome Readiness Tool

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MFA Is Bypassed. Here’s How Attackers Do It With Session Cookies
May 11, 2026

MFA Is Bypassed. Here’s How Attackers Do It With Session Cookies

MFA Stops Login Abuse. It Does Not Always Stop Session Theft.

Multi-factor authentication has become one of the most important controls in enterprise security. It reduces the risk of password-based compromise and makes it much harder for attackers to access applications using stolen credentials alone.

But MFA protects the authentication moment. It does not automatically protect every authenticated session that follows.

Once a user successfully signs in, the browser receives session cookies or session tokens that keep the user logged in across web applications. These tokens tell the application, “this user has already been authenticated.” If an attacker steals that session cookie, they may be able to impersonate the user without needing the password, the MFA code, or the user’s device.

This is why session cookie theft has become such a dangerous browser-layer threat. The attacker is not always trying to break MFA. They are trying to go around it.

How Attackers Bypass MFA With Session Cookies

Session cookie attacks usually begin after authentication has already happened. The user signs in normally, completes MFA, and receives a valid browser session. From that point onward, attackers target the session itself.

Common attack paths include:

  • Infostealer malware on the endpoint that extracts browser cookies and session data.

  • Malicious or unverified extensions that gain access to browser activity or sensitive session context.

  • Phishing pages and attacker-controlled domains that redirect users into credential or token theft workflows.

  • Outdated browsers that lack the latest protections against session theft and cookie abuse.

  • Long-running authenticated sessions where users remain logged in without frequent re-verification.

The key problem is that many enterprise controls still focus heavily on login events. But session theft happens inside the browser after the login event is complete.

That makes the browser a critical security boundary.

Why Traditional MFA-Centric Security Falls Short

MFA is still essential. The problem is assuming that MFA alone is enough.

In a session theft scenario, the attacker does not need to defeat the MFA prompt directly. They only need to steal the post-authentication token that the browser uses to maintain access. Once that token is replayed, the application may treat the attacker as the already-authenticated user.

This creates a visibility and enforcement gap. Identity systems can confirm that MFA was completed, but they may not always know whether the session token is still being used by the legitimate browser, on the legitimate device, under the right conditions.

For enterprises, this means browser posture matters just as much as identity posture. A user may have strong authentication, but if their browser is outdated, exposed to risky extensions, or accessing unsafe domains, the session remains vulnerable.

Chrome Enterprise Premium: Protecting the Browser Session

Chrome Enterprise Premium helps address this gap by bringing security controls closer to where session activity actually happens: the browser.

Chrome Enterprise Premium is a secure enterprise browsing solution that provides advanced, integrated security directly within the browser, including centralized management, threat and data protection, and Zero Trust access controls for web applications.

For session cookie risk, this matters because the browser is where authenticated sessions live. Chrome Enterprise Premium helps organizations strengthen browser-layer protection through capabilities such as malware and phishing protection, URL filtering, data protection controls, and access controls that reduce exposure across web and SaaS applications. Google’s product documentation describes Chrome Enterprise Premium as enhancing Chrome’s built-in enterprise security with configurable data loss prevention, threat protection, and secure enterprise browsing controls.

This is especially important when attackers use phishing, malicious domains, malware, or unsafe browser activity as the path to session theft. Chrome Enterprise Premium helps enforce protection at the point of browsing, instead of relying only on identity checks that already happened earlier in the session.

From Readiness Tool: Understanding Session Risk Across the Browser Fleet

Browser Insights, the Chrome Readiness Tool, gives security teams device-level visibility into browser risk before incidents occur.

Based on the current Browser Insights structure, the tool surfaces browser and extension details across Chrome, Edge, Firefox, Vivaldi, Brave, and Opera. This includes browser name, browser version, and all installed extensions.

For MFA bypass and session cookie theft, the most relevant signal is session theft vulnerability based on browser version. Outdated browsers are flagged as not protected, while current versions are confirmed as protected.

Browser Insights also shows the presence of unverified extensions, which is important because risky extensions can increase browser-layer exposure. A device is considered secure within Browser Insights when it has no unverified extensions and no access to restricted or non-HTTPS domains. The tool also supports device-level drill-down, allowing security teams to investigate specific machines where browser risk is elevated.

This makes the Chrome Readiness Tool valuable as a visibility layer. It helps security teams identify which devices, browsers, and extensions may increase the risk of session theft before attackers exploit that weakness.

Where CEP Accelerator Adds Value

CEP Accelerator turns Browser Insights findings into a prioritized Chrome Enterprise Premium deployment plan.

It does not enforce policies or detect attacks directly. Instead, it acts as a planning and visibility layer inside Browser Insights. It maps observed risks to the relevant CEP capabilities that can address them.

For MFA bypass through session cookies, this means security teams can connect findings such as outdated browser versions or unverified extensions to the CEP controls that help reduce session theft and unauthorized access risk. CEP Accelerator helps teams decide where to act first, instead of treating every browser issue as equal.

Closing the MFA Gap Starts in the Browser

MFA remains a critical defense, but it is not the final boundary. Once a session is created, attackers shift their focus from stealing passwords to stealing browser session tokens.

That makes browser visibility and browser enforcement essential.

Browser Insights helps identify where session-related risk exists across the enterprise browser fleet. Chrome Enterprise Premium provides the enforcement layer needed to strengthen browser security against phishing, malware, unsafe access, and data exposure. CEP Accelerator connects the two by helping security teams prioritize the right actions based on observed risk.

To reduce MFA bypass risk, start by finding the vulnerable browsers, outdated versions, and unverified extensions across your environment. Then use Chrome Enterprise Premium to bring protection closer to the session itself.

AI-Generated Zero-Days: What Your Security Team Needs to Know Now
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AI-Generated Zero-Days: What Your Security Team Needs to Know Now

A Structural Shift in How Vulnerabilities Are Found

The emergence of AI-assisted vulnerability research has altered the economics of zero-day discovery in ways that directly affect enterprise browser security planning. What previously required specialized expertise and significant manual effort, reviewing source code, fuzzing inputs, and analyzing crash reports, can now be assisted or partially automated using large language models and AI-driven fuzzing tools. The practical result is that zero-day vulnerabilities in browser components are being identified at higher frequency and with lower barriers to entry.

This shift matters for enterprise security teams because it compresses the timeline between a vulnerability existing and that vulnerability being discovered, weaponized, and used in attacks. The assumption that a zero-day requires nation-state resources to develop is increasingly outdated. AI tooling has made aspects of vulnerability research accessible to a much broader range of threat actors.

The browser is the primary target in this environment because it represents the convergence of user credentials, session tokens, enterprise application access, and sensitive data, all within a single process that is exposed to external content by design.

Where the Risk Comes From

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  • Large language models can assist in converting discovered crash conditions into working proof-of-concept exploits, reducing the time from discovery to weaponization

  • Browser credential stores and session tokens are high-value targets for zero-day exploitation because they provide immediate access to enterprise applications without requiring separate credential theft

  • Outdated browsers running across managed and unmanaged enterprise devices represent a persistent attack surface for both new and historical zero-days

  • Extension supply chain compromise allows attackers to deliver zero-day payloads through trusted extension update channels rather than requiring direct browser exploitation

Chrome Enterprise Premium: Defense Depth Against Unknown Vulnerabilities

Chrome Enterprise Premium provides multiple enforcement layers that limit zero-day impact even when the specific vulnerability is unknown. Site isolation ensures that even a successful exploit of a browser rendering component cannot automatically access session tokens and credentials associated with other origins in the same session. This architectural boundary constrains the scope of what an attacker gains from a zero-day exploit.

App-bound encryption protects stored credentials and session tokens at the browser process level. An attacker who successfully exploits a zero-day in a browser component gains a more limited foothold than in a browser without this protection, because credential extraction requires additional steps that CEP's controls are designed to obstruct.

CEP's extension governance capabilities allow organizations to enforce allowlist-based extension policies, blocking the delivery of zero-day payloads through compromised extension update channels before they reach end-user devices.

Understanding Risk with Chrome Readiness Tool

Browser Insights provides the fleet-wide visibility that security teams need to assess zero-day exposure. Session theft vulnerability is evaluated based on browser version: current browsers are confirmed as protected against known session theft mechanisms, while outdated browsers are flagged as not protected and represent the highest priority for remediation ahead of any zero-day campaign.

The tool surfaces installed extensions across Chrome, Edge, Firefox, Vivaldi, Brave, and Opera, identifying unverified and outdated extensions that represent both supply chain risk and potential zero-day delivery vectors. Security teams can use device-level drill-down to investigate specific machines where extension and browser version risk combine to create elevated exposure.

Unsecured domain access is flagged within Browser Insights as an additional risk signal. Non-HTTPS and restricted domains are common channels for exploit delivery, and their presence in the device risk profile indicates that CEP enforcement should be prioritized. A device is classified as secure when it has no unverified extensions and no access to restricted or flagged domains.

Where CEP Accelerator Adds Value

CEP Accelerator functions as a planning layer inside Browser Insights, connecting observed risk signals to the CEP capabilities that provide the most relevant defense against AI-generated zero-day threats.

For zero-day risk planning, CEP Accelerator helps security teams understand which devices carry the highest exposure based on browser version gaps and extension risk, and maps those findings to the specific CEP controls, including site isolation, app-bound encryption, and extension allowlist enforcement, that should be deployed first. It translates Browser Insights visibility into a prioritized enforcement action plan.

Preparing for Vulnerabilities That Have Not Been Announced Yet

Zero-day threats by definition arrive before defenses are tuned for them. The organizations best positioned to limit their impact are those that have deployed enforcement controls that constrain exploit impact without requiring vulnerability-specific knowledge. Chrome Enterprise Premium provides that enforcement foundation. Browser Insights identifies where it is most urgently needed.

Start by identifying risks with Browser Insights to understand where your device fleet is most exposed to the next browser-targeted zero-day campaign.

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When Patch Tuesday Is Too Slow: The Case for Browser Isolation

The Widening Window Between Discovery and Patch

The enterprise patch cycle was designed for a different threat environment. Monthly patch cycles made sense when vulnerability discovery was manual, slow, and resource-intensive. AI-assisted vulnerability research has changed that timeline fundamentally. Security researchers and threat actors alike can now identify exploitable flaws in browser engines, rendering components, and JavaScript environments at a pace that outstrips the traditional 30-day patch window.

For enterprise security teams, this creates a structural exposure problem. Between the day a vulnerability is identified and the day an enterprise can validate, package, and deploy a patch across a managed fleet, attackers can be actively exploiting that vulnerability against unpatched browsers. The browser, as the primary workspace for enterprise data access, SaaS application use, and credential handling, represents the highest-value target in this window.

Browser isolation addresses this gap not by accelerating the patch cycle but by reducing what an attacker can accomplish while that window is open. It is a risk reduction strategy for an era in which patch timelines and discovery timelines are fundamentally mismatched.

Where the Risk Comes From

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  • Browser engine exploits can provide direct access to session tokens, credential stores, and application data without requiring the attacker to compromise the endpoint separately

  • Outdated browsers running in managed fleets continue to access sensitive enterprise applications during the patch window, expanding the blast radius of unpatched vulnerabilities

  • AI-generated proof-of-concept exploits reduce the technical barrier for operationalizing newly discovered vulnerabilities before patches are available

  • Data exfiltration through browser-based exploits bypasses endpoint detection tools that are not positioned to inspect in-browser processes

Chrome Enterprise Premium: Isolation and Enforcement as a Risk Reduction Layer

Chrome Enterprise Premium provides browser-level controls that reduce the impact of unpatched vulnerabilities without requiring a patch to be deployed. Site isolation enforces process separation between different web origins, limiting the scope of what a successful browser exploit can access within a single session. This architectural control operates independently of whether the browser has received the latest security patch.

CEP's Safe Browsing integration and real-time URL classification prevent browsers from reaching the delivery infrastructure that exploit campaigns typically rely on. Even in a window where a browser vulnerability is known and unpatched, CEP's network-layer enforcement reduces the likelihood of successful exploitation by blocking access to the domains and resources used to deliver browser-targeted payloads.

App-bound encryption protects credential and session data from extraction even when a browser process has been partially compromised, limiting the post-exploitation value of a successful browser-level attack.

Understanding Risk with Chrome Readiness Tool

Browser Insights makes the patch gap visible at the device level. The tool assesses session theft vulnerability based on browser version, clearly distinguishing devices running current and protected browsers from those running outdated and not protected versions. This distinction is critical during any period when a known vulnerability is unpatched across the fleet.

Extension security is also surfaced within Browser Insights. Unverified and outdated extensions represent additional attack surface that can be exploited in combination with browser engine vulnerabilities. The tool covers Chrome, Edge, Firefox, Vivaldi, Brave, and Opera, providing fleet-wide visibility rather than a single-browser view.

Access to unsecured domains is a further risk signal, as non-HTTPS and restricted domains are frequent exploit delivery channels. A device is considered secure when it presents no unverified extensions and no access to restricted domains.

Where CEP Accelerator Adds Value

CEP Accelerator is a planning layer inside Browser Insights. It connects the risk signals surfaced by Browser Insights, specifically outdated browser versions and unverified extension exposure, to the CEP capabilities that mitigate patch-window risk.

During a period of known browser vulnerability, CEP Accelerator helps security teams identify which devices are most exposed and which CEP controls should be prioritized for rapid deployment. It turns the visibility provided by Browser Insights into a concrete enforcement action plan that does not wait for the patch to be available.

Reducing Exposure When the Patch Is Not Ready

Browser isolation and policy enforcement are not substitutes for patching, but they are essential for the period when a patch is not yet deployed. Chrome Enterprise Premium provides the controls that reduce exploitability and limit post-exploitation impact. Browser Insights identifies where those controls are most urgently needed.

Start by identifying risks with Browser Insights to understand which devices in your fleet are most exposed during the current patch window.

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How CEP Detects AI-Driven Workflows Versus Human Activity

When the Browser Can No Longer Assume a Human Is Driving

Enterprise browser security has historically been built around one assumption: a human is operating the browser. Behavioral analytics, anomaly detection, and access controls have been calibrated to human interaction patterns. AI-driven workflows break that assumption. Automated agents navigate applications, submit data, and access resources at speeds and scales that fall outside normal human behavior baselines, creating both detection gaps and new risk categories.

For security teams, the inability to reliably distinguish AI-driven activity from human activity is not just a monitoring problem. It is a control problem. If an enterprise cannot differentiate a sanctioned AI workflow from a malicious automated process operating inside a legitimate browser session, it cannot enforce meaningful restrictions on what that activity is permitted to do.

Chrome Enterprise Premium addresses this challenge through browser-level policy enforcement that applies uniformly to all activity, regardless of whether it is human or automated, and through administrative controls that allow organizations to govern what automation is permitted to operate within the browser environment.

Where the Risk Comes From

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Chrome Enterprise Premium: Policy That Governs All Browser Activity

Chrome Enterprise Premium enforces policy at the browser layer, which means it applies to all processes operating within that context, including AI agents. App-bound encryption ties credential and session token access to the specific browser process, preventing automated scripts or external tools from extracting session material even when they operate within an authenticated session.

CEP's extension management capabilities allow organizations to define an allowlist of verified extensions, blocking unverified automation tools from operating within the enterprise browser environment. This provides direct governance over what automation frameworks are permitted to interact with browser sessions and enterprise application data.

Administrative reporting surfaces unusual extension activity and policy violations regardless of whether the source is human or automated, giving security teams the operational visibility needed to identify unauthorized agent activity.

Understanding Risk with Chrome Readiness Tool

Browser Insights provides the foundational visibility needed to assess AI workflow risk across the device fleet. The tool reports installed extensions across Chrome, Edge, Firefox, Vivaldi, Brave, and Opera, flagging unverified and outdated extensions that may be introducing unauthorized automation capabilities into the enterprise environment.

Session theft vulnerability assessment is based on browser version. Current browsers are confirmed as protected; outdated browsers are flagged as not protected, representing risk that automated session hijacking can exploit. Browser Insights also surfaces access to non-HTTPS and restricted domains that AI-driven workflows should not be reaching.

Device-level drill-down allows security teams to investigate specific machines where the combination of unverified extensions and outdated browsers creates the highest risk of unauthorized automated activity.

Where CEP Accelerator Adds Value

CEP Accelerator functions as a planning and visibility layer inside Browser Insights. It does not detect AI-driven activity directly or enforce policies autonomously. What it does is connect the risk signals observed in Browser Insights, such as unverified automation extensions or vulnerable browser versions, to the specific CEP capabilities that govern those risks.

For teams assessing AI workflow security, CEP Accelerator helps prioritize enforcement: which devices need immediate browser updates, which extension policies need to be deployed first, and where CEP's session protection controls will have the highest impact. It turns visibility into an actionable enforcement roadmap.

Governing the Automated Browser Enterprise

The boundary between human and AI-driven browser activity will continue to blur as enterprise adoption of agentic tools accelerates. Browser security strategy needs to account for this shift at the policy layer, not just at the detection layer. Chrome Enterprise Premium provides that policy foundation. Browser Insights provides the visibility to identify where it is needed most.

Start by identifying risks with Browser Insights to understand where unauthorized automation and session vulnerability intersect across your device fleet.

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