Key takeaways

• A VPN is a point-to-point encrypted tunnel that extends network access to a remote device. SASE is a cloud-delivered, converged framework — SD-WAN plus "zero trust network access" (ZTNA), SWG, CASB, DLP, and RBI — that grants identity-based access to individual applications instead of the whole network.
• VPNs authenticate once and then trust broadly, which is why VPN and edge-device exploitation grew from 3% to 22% of initial access vectors year over year, according to the Verizon 2025 DBIR.
• SASE narrows that trust model with ZTNA, but it still routes traffic through a central inspection point, a cloud proxy instead of a data center, which runs into the same limits as encryption and AI-driven work evolve.
• Neither architecture sees inside the browser session itself, where most enterprise work (SaaS, internal apps, AI tools) now happens. 95% of enterprises have experienced browser-based attacks that bypassed network and endpoint controls, per VentureBeat.
• The practical decision for IT and security leaders isn't VPN versus SASE in isolation. It's where enforcement needs to move next, closer to the actual point of work, at the browser and endpoint layer, alongside existing SASE and identity investments.

Introduction

Every enterprise security leader eventually asks a version of the same question: why does our remote access architecture still feel like it's fighting yesterday's threats? VPNs were built for a world of on-premises data centers. SASE emerged to modernize that model for the cloud era.

Both terms get used loosely, sometimes interchangeably, in vendor conversations and RFPs. But they solve the same underlying problem, secure remote access, from different points in the network stack, with different assumptions about trust and enforcement.

This article walks through what each does, where SASE improves on VPN, and where both still share a blind spot that matters for anyone planning next year's security architecture.

The short answer

A VPN is a dedicated, encrypted tunnel between a remote endpoint and a corporate network. Once authenticated, the device is effectively inside that network, with access governed by whatever segmentation the network team has configured.

SASE, short for "secure access service edge," is a cloud-delivered, converged framework rather than a single tunnel. It combines SD-WAN with a security stack: "zero trust network access" (ZTNA), "secure web gateway" (SWG), "cloud access security broker" (CASB), "data loss prevention" (DLP), and "remote browser isolation" (RBI), delivered from cloud points of presence. Instead of granting network-level trust, SASE evaluates identity and context to grant access to specific applications.

The distinction matters beyond vendor selection. It determines where policy gets enforced, how much lateral movement is possible after a breach, and how well the architecture matches where work happens now, largely in SaaS applications and browsers rather than on-premises servers.

What a VPN does

Built for a data-center world

VPNs were the right architecture when enterprise applications lived on-premises and remote employees were the exception, not the rule. Extending the corporate perimeter to a remote laptop made sense when the destination, the application, sat inside that same perimeter.

Why VPNs strain under modern work

That architecture strains under two pressures. First, VPNs typically grant broad network-level access once a user authenticates, rather than access scoped to a specific application, a pattern that increases lateral-movement risk if a credential or device is compromised, a point covered in more detail in secure remote access belongs in the browser.

Second, most applications enterprises rely on today are SaaS or cloud-hosted, not on-premises. Routing traffic through a VPN to reach a network that no longer holds the application creates unnecessary backhaul and latency. Related patterns for remote access security beyond VPN outline how this shows up operationally.

VPN appliances have also become a favored attack target. CISA ordered federal agencies to disconnect Ivanti VPN appliances in 2024, affecting more than 2,200 devices. CISA issued a similar three-day patch mandate after a Check Point VPN zero-day surfaced in 2026, per its known exploited vulnerabilities catalog. The Verizon 2025 DBIR quantifies the trend: VPN and edge-device exploitation grew from 3% to roughly 22% of initial access vectors year over year, an eightfold increase.

What SASE adds on top of VPN

Convergence and identity

SASE, a term Gartner introduced in its 2019 report "The Future of Network Security Is in the Cloud," converges SD-WAN with a full security stack delivered from the cloud. ZTNA replaces implicit network trust with per-application, identity-driven access. That's a foundational shift covered in core security principles behind SASE. Gartner projects the SASE market will reach $28.5 billion by 2028, growing at a 26% compound annual rate, and reports 63% of organizations worldwide have already implemented a zero trust strategy.

Under SASE, identity functions as the perimeter. Access decisions incorporate device posture, user role, and context rather than simply confirming the device sits on the right network segment. This is a meaningful improvement in granularity over a traditional VPN.

Where SASE still shares a VPN-era assumption

Even with that improvement, SASE and its narrower sibling SSE still route traffic through a central enforcement point, a cloud proxy instead of a data center tunnel, and inspect it there. That model assumes traffic can be decrypted, inspected, and forwarded. Modern encryption standards like TLS 1.3 strain that assumption; TLS 1.3 removed the RSA key exchange that made passive inspection easier. AI-driven, agentic workflows strain it further, since they don't behave like conventional web traffic. The distinction between SASE and SSE and where assumptions no longer hold in SASE go into more depth on this specific limitation.

VPN vs SASE: a side-by-side comparison

The gap neither one closes: the browser session

Both architectures stop at the network or connection layer. Neither one sees what happens once access is granted, inside the browser tab where the work itself occurs. Copy-and-paste into an unsanctioned destination, unmanaged file downloads, prompts submitted to an AI tool, or a screenshot of sensitive data all happen after the VPN tunnel or SASE policy has already done its job.

This gap has measurable consequences. 95% of enterprises have experienced browser-based attacks that bypassed network and endpoint controls, according to VentureBeat. Gartner estimates more than 85% of enterprise work now happens inside the browser or SaaS applications. Secure remote access enforced at the wrong layer and why remote access strategies miss the browser cover this shift in more detail, and why network ZTNA isn't enough makes the same case specifically against the zero trust network layer.

This isn't an argument to rip out VPN or SASE investments. It's an argument that the next layer of enforcement needs to sit closer to where the work happens, the browser session and the endpoint, as a complement to network and identity controls already in place.

What this means for enterprise IT and security leaders

For most organizations, the choice isn't strictly VPN or SASE. Legacy on-premises applications may still warrant a VPN in the near term. A broader shift to cloud and SaaS applications justifies SASE's identity-first model. But both leave the same last-mile gap open, and closing it means adding enforcement at the browser and endpoint layer. Island Enterprise Network, for example, applies ZTNA, SWG, CASB, DLP, and RBI directly at the browser and endpoint rather than relying solely on network-level enforcement, as described in Island Enterprise Network.

The architectural decision worth making now isn't which acronym to standardize on. It's deciding where policy gets enforced, and matching that decision to where work happens today, not where it happened a decade ago.

FAQs

Do we need to replace our VPN with SASE, or can they coexist?

They typically coexist. Most enterprises retain VPN access for legacy on-premises applications while adopting SASE's ZTNA model for cloud and SaaS traffic. The two aren't mutually exclusive architectures. SASE is often layered in alongside existing VPN infrastructure rather than replacing it outright, at least until legacy app access is fully migrated or retired.

If we've already implemented SASE, are we still exposed to the risks described here?

Partially. SASE's ZTNA component meaningfully reduces the broad network trust problem that makes VPNs risky, but SASE still centralizes inspection at a cloud proxy rather than at the point of work. That means session-level activity inside the browser, data exfiltration via copy and paste, unmanaged downloads, AI tool usage, remains outside SASE's visibility, the same limitation it inherited from VPN architectures.

Does moving to SASE reduce our attack surface compared to VPN appliances?

Yes, in terms of exposed infrastructure. SASE reduces the number of internet-facing VPN appliances, which have been a frequent target for CVE exploitation. The Verizon 2025 DBIR reported an eightfold increase in VPN and edge-device exploitation as an initial access vector. However, the centralized cloud proxy in a SASE architecture becomes its own consolidated target, so attack surface shifts rather than disappears.

How does encryption like TLS 1.3 affect SASE's inspection capabilities?

TLS 1.3 removed the RSA key exchange that made passive traffic inspection straightforward, which constrains how much a SASE proxy can decrypt and inspect without active interception techniques. This is one reason SASE's central-inspection model runs into the same structural limits as VPN as encryption standards and AI-driven traffic patterns evolve.

Where does browser-based enforcement fit relative to our existing SASE deployment?

It's additive, not a replacement. Browser and endpoint-layer enforcement, such as what Island Enterprise Network applies through ZTNA, SWG, CASB, DLP, and RBI directly at the session level, closes the last-mile gap that sits downstream of both VPN and SASE policy decisions. It complements identity and network controls already in place rather than requiring a rip-and-replace of SASE investments.

What's a reasonable first step for evaluating this gap in our own environment?

Start by mapping where sensitive data moves today. Most of it now happens inside browser sessions and SaaS applications rather than on the network. Reviewing incident data for browser-based attacks that bypassed existing network and endpoint controls, VentureBeat reports 95% of enterprises have experienced this, is a useful baseline for deciding whether additional session-level visibility is warranted before your next architecture review.

See where enforcement fits next

If your VPN and SASE investments still leave the browser session as a blind spot, that's worth a closer look before your next architecture cycle. Schedule a demo to see how Island applies ZTNA, SWG, CASB, DLP, and RBI directly at the point of work, and how it fits alongside what you've already deployed.