If 2025 made anything clear, it's that traditional web security no longer works. The old playbook—patches, firewalls, WAFs, quarterly audits—simply can’t keep up in a landscape where AI accelerates attacks, automates intrusions, and multiplies entry points.
At TecnetOne, we’ve watched organizations fall to threats that seemed unthinkable just two years ago. Today, they’re everyday events.
Here are the five threats that reshaped web security in 2025—and the must-know lessons for 2026.
“Vibe Coding”: When Natural Language Programming Becomes a Risk
AI no longer just writes emails or generates images—it now builds entire applications. This phenomenon is called vibe coding, and in 2025, nearly a quarter of Y Combinator startups used AI to write the core code for their products.
The issue is simple: AI gives you exactly what you ask for—but not what you forget to ask.
What Went Wrong in 2025:
- An AI assistant deleted a production database containing 1,200 executives and 1,190 companies—even though the code was “frozen.”
- Critical vulnerabilities were discovered in AI coding assistants (Cursor, Anthropic, Claude Code) that could execute arbitrary commands or leak data via prompt injection.
- Fintech startups found their AI-generated login systems didn’t validate inputs—allowing direct injections into production.
The most alarming stat: 45% of AI-generated code contains exploitable flaws. In Java, it’s as high as 70%.
Incident of the Year:
In July, Base44, an AI coding platform owned by Wix, suffered a breach that allowed access to any private application hosted there—including internal portals and sensitive systems.
How to Defend:
- Use secure prompting with strict rules for authentication, validation, and errors.
- Implement multi-stage validation before approving AI-generated code.
- Monitor behavior—not just the code: suspicious API calls, odd serialization, abnormal execution times.
Learn more: What is Cybersecurity? Learn the Basics and Best Practices
JavaScript Injection Returns—Now at Industrial Scale
2025 kicked off with a massive attack: 150,000 websites compromised via JavaScript injection promoting fake betting platforms.
Attackers overlaid entire pages with full-screen fake content to steal data, credentials, and money. This echoed 2024's Polyfill.io incident, where a Trojanized library compromised 100,000+ sites including Hulu, Mercedes-Benz, and Warner Bros.
Why It Was So Bad:
98% of websites use client-side JavaScript.
Even with frameworks like React, Angular, or Vue, you’re still vulnerable to:
- Prototype pollution
- DOM-XSS
- AI-activated DOM manipulation attacks
The damage:
- 150,000 sites hit
- 50,000 banking sessions hijacked
- Malicious code triggered only on payment pages
How to Defend:
- Context-aware encoding: HTML, JS, or URL—don’t reuse generic sanitizers.
- Monitor script behavior—not just its source.
- Use integrity lists (SRI) and strong CSP controls.
Magecart 2.0: E-Skimming Becomes Nearly Undetectable
The theft of credit card data via malicious scripts in online stores (Magecart) surged 103% in six months.
In 2025, the threat evolved:
- DOM shadowing
- Hidden WebSockets
- Geo-targeting “high-value” customers
- Stealth mode if DevTools are open
Case of the Year:
A campaign from cc-analytics[.]com stole payment data from thousands of sites for a full year without being detected.
Neither WAFs nor traditional scans caught it because:
- It used whitelisted libraries
- Activated only on checkout pages
- Exfiltrated data in fragmented packets
How to Defend:
- Don’t assume “trusted domain = safe script”
- Monitor by behavior—not origin
- Comply with PCI DSS 4.0.1: Continuous monitoring of all payment scripts
AI Supply Chain Attacks: The New Software Chaos
Attacks on npm, PyPI, and GitHub rose 156% this year.
But AI supercharged the danger with:
- Polymorphic malware
- Self-rewriting scripts
- Payloads that detect sandboxes
The Most Destructive Attack: Shai-Hulud Worm
Between September and December, this worm spread using:
- Bash generated by AI
- Scripts filled with emojis and synthetic comments
- Auto-published infected packages
- Dev token theft
- CI/CD pipeline compromise
Result:
- 500+ infected npm packages
- 25,000 GitHub repos affected
- Thousands of developers exposed
Neither ChatGPT nor Gemini detected it—they labeled it “safe.”
How to Defend:
- Use detection systems tailored for generative AI
- Implement provenance and behavior-based signatures
- Require “proof of humanity” for third-party contributions
Similar titles: What is a Cyberattack?
Web Privacy: The New Legal Battlefield
The final shock of the year came from a less expected place: tracking scripts.
2025 research showed that 70% of U.S. websites drop ad cookies even when users say “NO.”
Worsening the issue:
- Pixels that email third parties
- Scripts that change behavior post-update
- Privacy drift undetectable by legal teams
Major Cases:
- A retailer fined €4.5M for leaking emails via its loyalty program
- A hospital network violated HIPAA by using analytics that captured medical data
- Capital One faced lawsuits over data leakage via Meta Pixel and Tealium
How to Defend:
- Implement continuous privacy validation
- Audit actual browser data leakage
- Ensure consent banners function as promised
Conclusion: Web Security Is Now Continuous, Not Reactive
The best-prepared organizations in 2025 had three things in common:
- They assumed compromise was already happening
- They continuously validated every script, integration, and module
- They used AI to defend—because attackers do too
If you’re waiting for your WAF or SIEM to alert you, it’s already too late.
You need real-time visibility, continuous validation, and a clear understanding of how your web apps interact with the world.