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Client-Side Attack Recap – Q1 2025

Wednesday, April 30th, 2025

Updated May 1st, 2025

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Simon Wijckmans

Authored by: c/side Threat Research Team

Executive Summary

Q1 2025 was marked by a sharp escalation in client-side attacks targeting websites across multiple industries, with a particular focus on WordPress-powered platforms. c/side’s research uncovered nearly 300,000 compromised websites, highlighting a growing reliance by attackers on JavaScript-based delivery mechanisms, third-party supply chain vulnerabilities, and deceptive social engineering tactics such as fake browser updates.

For CISOs, digital risk leaders, and security stakeholders, this report outlines the most critical campaigns detected this quarter, presenting both technical detail and strategic insight to support proactive decision-making.

Key Insight for Executives: Modern cyber threats now exploit browser-based interactions and user trust in common CMS platforms. Defending against them requires visibility into runtime behaviors, rigorous script governance, and coordinated threat intelligence. Additionally, client-side attacks targeting cryptocurrency platforms and payment environments pose outsized risks, despite representing a smaller volume of total incidents.

Major Client-Side Campaigns

1. Full-Page Hijacks Redirecting to Chinese Gambling Sites

  • Detected: January 2025
  • Websites Impacted: 150,000+
  • Root Cause: JavaScript injected via hijacked plugin or asset CDN.
  • Attack Infrastructure: Domains like zuizhongyj[.]com and its subdomains were responsible for injecting iframes that took over the entire viewport.
  • Notable Traits:
    • Conditional redirection based on region and browser
    • Script obfuscation and dynamically constructed URLs
    • High mobile focus with Android-targeted click-throughs
  • Strategic Risk: Significant loss of trust and SEO penalties; several sites blacklisted by Google.
  • https://cside.dev/blog/over-150k-websites-hit-by-full-page-hijack-linking-to-chinese-gambling-sites

2. JavaScript Supply Chain Compromise (4 Embedded Backdoors)

  • Detected: January 2025
  • Websites Impacted: 5,000+
  • Payload Origin: cdn.csyndication[.]com (formerly trusted asset hosting provider).
  • Embedded Malicious Actions:
    • Plugin installation for persistent access
    • wp-config.php infection
    • SSH key injection via scheduled tasks
    • Reverse shell communication to gsocket[.]io
  • Adversary Goals: Maintain long-term control, harvest credentials, and pivot laterally across shared hosting environments.
  • https://cside.dev/blog/thousands-of-websites-hit-by-four-backdoors-in-3rd-party-javascript-attack

3. Kaiyun Chinese Gambling Scam – Variant Campaign

  • Detected: February 2025
  • Websites Impacted: 35,000+
  • Tactics: Mimicked legitimate gaming advertisements via full-screen overlays and used geo-targeted language variants.
  • Key Observations:
    • Domain reuse: mlbetjs[.]com, zuizhongjs[.]com
    • IP and browser profiling to evade detection
  • Outcome: Brand confusion and conversion siphoning for affected commercial websites.
  • https://cside.dev/blog/over-35-000-websites-targeted-in-full-page-hijack-linking-to-a-chinese-language-gambling-scam

4. Fake Browser Update Campaign with Cross-Platform Malware

5. ScriptAPI SEO Poisoning on Academic and Government Sites

  • Detected: January 2025
  • Websites Impacted: ~1,000
  • Target Profile: .edu and .gov domains using outdated JS bundles
  • Attack Behavior: Hidden DOM injections for SEO link building; cloaked redirections to gambling and adult content
  • Business Impact:
    • Algorithmic demotion in SERPs
    • Abuse of academic/governmental trust for backlink poisoning
  • https://cside.dev/blog/government-and-university-websites-targeted-in-scriptapi-dev-client-side-attack

6. WP3.XYZ Campaign – Automated WordPress Backdoor Creation

  • Detected: January 2025
  • Websites Impacted: 5,000+
  • Initial Vector: JS script from wp3[.]xyz included in compromised themes/plugins
  • Key Findings:
    • Silent creation of wpx_admin account
    • Plugin deployment to modify login flows
    • Exfiltration of credentials and tokens
  • Remediation: Requires admin credential rotation, malware cleanup, and plugin verification
  • https://cside.dev/blog/over-5k-wordpress-sites-caught-in-wp3xyz-malware-attack

Strategic Recommendations for Executives and CISOs

  1. Client-Side Risk Governance: Mandate pre-deployment reviews and post-deployment monitoring for all third-party JavaScript assets.
  2. Runtime Detection Capabilities: Invest in behavior-based monitoring of web pages to catch threats like iframing, credential theft, or redirection chains.
  3. Web CMS as a High-Value Target: WordPress, despite being widely used, requires enterprise-grade attention with automated patching and plugin vetting.
  4. Zero Trust for Content Delivery: Apply Zero Trust principles to JS scripts. Assume compromise and log every interaction.
  5. Response Playbooks & Simulations: Create tabletop exercises for supply chain attacks, client-side injection, and credential compromise based on real scenarios.

Key Metrics Overview

Metric

Q1 2025 Outcome

Total Websites Compromised

Nearly 300,000

New Client-Side Attack Techniques Observed

5 (iframe hijack, SEO poisoning, cross-platform malware, etc.)

Major Supply Chain Compromises

2

Predominant CMS Targeted

WordPress

Top Affected Industries

Ecommerce, Media, Government, Academia

Regulatory Exposure

GDPR, CCPA non-compliance risks

Compliance Risks Highlighted

PCI-DSS, GDPR, CCPA

Crypto Sector Targeting

Low volume, High financial impact

Number of Websites Impacted by Attack Type

During Q1 2025, several important strategic patterns emerged across client-side attack activity:

1. Rise of Cross-Platform Threats

  • Attacks are no longer targeting just Windows users. Malware campaigns (e.g., AMOS Stealer) expanded aggressively into macOS ecosystems, signaling an evolution toward cross-platform targeting.

2. Abuse of Trusted Supply Chains

  • The compromise of cdn.csyndication[.]com demonstrates that attackers increasingly target reputable third-party vendors to maximize impact at scale.
  • Supply chain attacks now extend beyond software to asset delivery infrastructures (JavaScript/CDNs).

3. Increased Sophistication in Evasion Techniques

  • Widespread use of:
    • IP geofencing
    • Browser fingerprinting
    • Mobile prioritization to evade automated detections and increase user targeting precision.

4. Proliferation of SEO Poisoning

  • Attacks increasingly abuse high-authority domains (e.g., .edu, .gov) for search engine poisoning, aiming for indirect monetization instead of direct exploitation.

5. WordPress Remains the #1 Attack Surface

Despite years of awareness, unpatched WordPress plugins/themes continue to be the primary entry point for large-scale compromises.

Compliance and Regulatory Impact

Client-side compromises, especially those delivering malware or misusing personal information, trigger serious compliance risks.

1. General Data Protection Regulation (GDPR)

  • Malware-laden redirects or compromised websites can be interpreted as a breach of data security obligations under GDPR Article 32.
  • Potential fines up to €20 million or 4% of global turnover, whichever is higher.

2. PCI-DSS Risk: Client-Side Payment Compromises

Client-side skimming attacks like Magecart and Formjacking create direct violations of PCI-DSS v4.0 requirements. Organizations processing cardholder data must secure client-side scripts to prevent unauthorized interception. Breach of this environment could result in:

  • Mandatory disclosure under PCI guidelines
  • Hefty fines
  • Brand and trust damage among customers

Given the prevalence of JavaScript-based attacks, securing the browser-side environment is now essential for PCI compliance.

3. California Consumer Privacy Act (CCPA)

  • Websites unintentionally serving malware or phishing may face private right of action lawsuits and regulatory penalties under CCPA.

  • Organizations that fail to secure client-side assets risk:
    • Customer lawsuits
    • Reputational loss
    • Delisting from advertising and search engine platforms (Google, Microsoft)

Risk Forecast for Q2 2025

Based on attack trends observed in Q1, c/side forecasts the following developments for Q2:

Forecasted Trend

Likelihood

Description

Rise of AI-Enhanced Client-Side Phishing

High

Attackers likely to use AI to craft dynamic fake update modals and fake login pages.

Expansion into Mobile App Supply Chains

Medium

Similar supply chain attacks may start targeting app SDKs and mobile-focused libraries.

SEO Poisoning Campaign Growth

High

Abuse of academic and governmental sites for SEO manipulation is expected to continue.

CDN and Plugin Supply Chain Targeting

High

Attackers will continue to compromise popular asset hosts and WordPress plugins.

Emergence of Cryptomining JavaScript Attacks

Medium

Dormant trend may resurge in Q2 targeting unmonitored browser sessions.


Targeted Crypto Wallet Drainer Campaigns

Medium

Attackers will prioritize high-value crypto targets despite low overall volume. Losses per incident could be catastrophic.

Strategic Recommendations for Executives and CISOs

Organizations must evolve from traditional perimeter defenses to real-time browser security monitoring. Here are c/side’s actionable recommendations:

1. Client-Side Risk Governance

  • Establish formal policies for pre-deployment review and continuous monitoring of all third-party JavaScript assets.
  • Maintain an inventory of approved scripts with versioning and integrity checks.

2. Runtime Detection Capabilities

  • Implement behavior-based monitoring of live website activity:
    • Detect iframe injections
    • Monitor DOM manipulation events
    • Flag unauthorized outbound connections
  • Solutions should alert on suspicious behaviors before users are impacted.

3. Zero Trust for Third-Party Content

  • Treat all external content as untrusted by default:
    • Apply CSP (Content Security Policy) headers to restrict loading of unapproved assets.
    • Use Subresource Integrity (SRI) to verify script integrity.

4. Enhanced WordPress Security Posture

  • Require automated patching for all plugins and core WordPress updates.
  • Mandate the use of vetted, high-quality plugins and themes only.
  • Monitor administrative account creations for anomalies.

5. Prepare and Test Incident Response Playbooks

  • Conduct regular tabletop exercises focused on:
    • Client-side script compromise
    • Supply chain breach scenarios
    • SEO poisoning cleanup
  • Include communication workflows for rapid disclosure to regulators if required (GDPR, CCPA).

Final Words

The threat landscape in early 2025 reflects a paradigm shift: attackers no longer need to breach infrastructure. They just need to compromise a script. The front-end is the new battlefield. Organizations must evolve beyond server-side defenses and embrace proactive, real-time client-side security strategies. Defenders must recognize that even low-frequency threats, such as crypto asset compromises and card skimming, carry the potential for outsized impact. Defense strategies must prioritize both volume-based and high-value, low-frequency attack scenarios.

c/side continues to monitor and publish emerging threats to empower defenders and protect digital trust.

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More About Simon Wijckmans

Founder and CEO of c/side. Building better security against client-side executed attacks, and making solutions more accessible to smaller businesses. Web security is not an enterprise only problem.