Malicious JavaScript Injected into Your Website: A Recovery Plan

Identify where the unwanted script enters the page

An injected script may come from a changed template, database content, a compromised plugin, a tag manager or an external supplier. Start by recording the affected URLs, discovery time, browser behaviour and suspicious network destinations without submitting genuine customer information. Preserve representative page source and relevant files in a controlled investigation copy.

Compare the server response with what the browser renders. A script absent from the initial HTML can still be introduced later by another script. Review the request chain and the component responsible for each unexpected request. Avoid fetching unknown payloads on an ordinary staff device; use an appropriately isolated analysis environment and escalate unfamiliar code to a qualified responder.

OWASP highlights that third-party JavaScript can change the behaviour of the page and expose information available within it. Therefore, a trusted-looking script hostname is not enough: review the current script, its source of authority and the account that can publish changes.

Protect visitor workflows while investigation continues

Prioritise pages collecting information: logins, enquiry forms, account profiles and checkout steps. If their integrity is uncertain, restrict the affected functions or replace them with a clean alternative agreed by the business owner. A working padlock only describes the encrypted connection; it does not establish that the scripts delivered through that connection are trustworthy.

1. Capture relevant evidence and record which visitor journeys may have been affected before removing the script.
2. Pause the suspected tag, integration or publishing route through a trusted administrator account. Check whether the same source is present on other pages or domains.
3. Review account access, publication history and deployment records for the component that introduced the code. Revoke unauthorised access and replace exposed credentials through trusted channels.
4. Assess the information that the affected page could access and involve the privacy or payment-service owner where relevant. Do not assume that deletion of the script resolves the earlier exposure.

Keep customer and staff communications consistent with the evidence. If the incident is still being scoped, say what is being investigated and which service has been restricted rather than claiming that no information could have been affected.

Repair the source and every delivery layer

Replace altered executable assets from reviewed source or trusted vendor releases. Where database fields contain injected markup, identify their intended purpose and validate the change carefully; broad search-and-replace can damage legitimate content or remove evidence. For a tag-manager incident, restore a reviewed configuration and examine who can publish future versions.

After the underlying source is corrected, purge or invalidate affected application and CDN caches through the normal provider workflow. Verify that browser requests receive the repaired asset version. A clean origin with an old cached response can make an incident appear unresolved, while a clean cached response can temporarily conceal a compromised origin.

Maintain an inventory of scripts that remain necessary. Record their owner, business purpose, loading conditions and any information they access. Retire abandoned marketing tags instead of keeping them merely because they were present in the old page. Test a replacement supplier as carefully as the component it replaces.

Use CSP as an additional control, with a tested rollout

OWASP describes Content Security Policy as an additional browser protection and distinguishes an enforced policy from a report-only policy. A report-only rollout can help identify legitimate dependencies before enforcement, but it does not itself block unwanted execution. Choose a policy suited to the application rather than pasting a generic header into production.

Review permitted script origins, inline execution requirements and how deployment changes update hashes or nonces where those controls are used. A policy that broadly trusts every existing source may retain the route that mattered in the incident. Conversely, tightening it without functional testing may break booking, accessibility or payment features that the business still needs.

Verify actual browser behaviour and document the findings

In a hypothetical case, a professional-services site has clean PHP templates but an unauthorised analytics-container change. Replacing the website files leaves the unwanted script in place because the container remains authorised to publish it. The successful repair removes the unauthorised change and access, then verifies the full browser request chain across the affected forms.

• Test representative pages in clean browsers and relevant consent states using synthetic data.
• Check request destinations, unexpected redirects, form actions and dynamically inserted scripts.
• Verify repaired assets after cache invalidation and a normal deployment cycle.
• Review privileged publishing changes and newly added integrations after reopening.
• Keep the assessed exposure period, evidence limitations and communication decisions in the incident record.

Escalate suspected skimming, heavily obfuscated code or incidents involving several script suppliers. CyberXperts can help investigate malicious JavaScript injection and coordinate the application, account and visitor-impact questions without relying on a visual page check alone.