Persistent HTML Injection: UI Redressing and Content Spoofing in Critical National Infrastructure

At XECbuild, we frequently observe enterprise and government entities investing heavily in perimeter defenses while overlooking the security posture of third-party integrations. Chatbots and virtual assistants, designed to streamline customer support, are increasingly becoming primary attack vectors when input sanitization is neglected.

Recently, during a targeted analysis of a highly-trafficked Government of India (GoI) portal responsible for handling sensitive citizen data, our methodology uncovered a critical Persistent HTML Injection and Content Spoofing vulnerability.

This case study illustrates how failing to sanitize chatbot inputs can allow threat actors to weaponize a trusted national domain for highly convincing phishing campaigns.

🔍 The Architectural Target: Virtual Assistants

Modern web applications integrate virtual assistants to guide users by rendering text, hyperlinks, and basic formatting. To function correctly, these bots must process user input. However, if the application architecture blindly trusts this input and echoes it back to the client without strict server-side sanitization, it creates a direct vector for injection attacks.

During our assessment of the GoI portal, the focus was strictly on the chatbot interface's input validation mechanisms.

⚙️ The Vulnerability: Bypassing the WAF

Initial testing revealed that while the perimeter Web Application Firewall (WAF) successfully intercepted standard Cross-Site Scripting (XSS) payloads (e.g., <script> execution), the underlying application completely failed to sanitize fundamental HTML tags.

By injecting basic formatting syntax, the application rendered the markup exactly as intended. This confirmed a critical architectural flaw: the virtual assistant was treating user-supplied input as executable HTML rather than safe text. While JavaScript execution was blocked, the HTML injection vector remained wide open.

⚠️ The Exploit: UI Redressing and Content Spoofing

Finding HTML injection is only the first step; demonstrating enterprise risk requires proving business impact. Because arbitrary HTML could be injected, the vulnerability was leveraged to execute a UI Redressing (Content Spoofing) attack.

By injecting a specifically crafted HTML and media payload, the trusted chat window was manipulated to display a highly realistic "Session Expired" overlay and administrative prompt.

The Business Risk:
The severity of this vulnerability is amplified by the context of the domain. Because the chatbot is hosted on a highly trusted, official .gov.in domain, any rendered HTML inherits that trust.

An advanced persistent threat (APT) or malicious actor could utilize this flaw to inject fraudulent login forms directly into the chat window. Citizens, implicitly trusting the national portal, could be easily tricked into submitting passwords, personal identification numbers, or financial details. Furthermore, because the injected form lives on the legitimate domain, standard anti-phishing filters and browser warnings would completely fail to flag the attack.

🏆 Responsible Disclosure to NCIIPC

As an ethical security organization, our priority is securing critical infrastructure, ensuring zero disruption to live services and absolutely no exposure of citizen data. Testing was immediately halted upon establishing the Proof of Concept (PoC).

A comprehensive vulnerability disclosure report, detailing the UI redressing payloads and the exact remediation steps, was compiled and submitted directly to the National Critical Information Infrastructure Protection Centre (NCIIPC), the nodal agency responsible for protecting India’s critical infrastructure.

The Key Takeaway for Enterprises:
Third-party integrations like chatbots must be subjected to the same rigorous security auditing as core infrastructure. Organizations must adopt a zero-trust approach to user input, enforcing context-aware client and server-side encoding, and implementing a strict Content Security Policy (CSP) to dictate where forms and media can be rendered.