The most common client-side attacks include credit card skimming (like Magecart attacks). But theft of session tokens through client-side scripts, malicious redirects, or general sensitive high-value data exfiltration are on the rise. These attacks have affected major companies, like British Airways and Ticketmaster with over 380,000 documented attacks in 2025 alone so far. A more recent example is the 2026 AppsFlyer SDK supply-chain compromise, where a single trusted third-party script delivered a polymorphic crypto stealer to many sites at once. Client-side attacks are often highly dynamic and targeted to prevent detection. Flying below the radar by only injecting malicious payloads under certain circumstances. They only fire at specific times, request locations, or user agents, making them nearly impossible to detect with traditional security tools.
How do client-side attacks actually happen?
Compromising a third-party service your website relies on is one common way attackers get in.
Why can't traditional security tools detect client-side threats?
Firewalls, WAFs, and vulnerability scanners are traditional security tools used to protect your server, but they cannot see what's happening in your users' browsers.
What's the difference between client-side security and server-side security?
Server-side security protects your infrastructure, while client-side security focuses on where your application actually runs, inside your users' browsers.
What's the difference between client-side security and application security?
Client-side security is a critical subset of AppSec that focuses on protecting applications where they actually execute--in users' browsers.