Listen to this Post
Introduction:
A seemingly innocuous experiment with an AI chatbot led to the discovery of a critical HTML injection vulnerability, demonstrating that even modern, well-defended platforms can fall prey to simple markup tricks. This security flaw allowed a researcher to embed fully rendered deceptive content, such as fake login forms, directly within chat conversations and shared links. The case underscores a fundamental security principle: where direct script execution (XSS) is blocked, attackers will pivot to lower-hanging fruit like content injection to manipulate user perception and trust.
Learning Objectives:
- Understand the methodology of pivoting from a blocked attack vector (XSS) to a successful one (HTML injection).
- Learn how to craft and test basic HTML injection payloads to probe for rendering vulnerabilities.
- Recognize the real-world impact of “deceptive UI” vulnerabilities in shared or public contexts.
You Should Know:
- The Hacker’s Mindset: Pivoting from XSS to HTML Injection
Step‑by‑step guide explaining what this does and how to use it.
When conventional attacks fail, ethical hackers shift strategy. In this case, the researcher began with standard Cross-Site Scripting (XSS) tests, injecting `` and similar payloads into the chat. The platform’s filters correctly blocked them. Instead of giving up, the researcher pivoted to testing for HTML injection—a less severe but still impactful vulnerability where user input is rendered as HTML elements without script execution. This involves testing if basic HTML tags are processed by the front-end.
How to Test:
- Environment: Use a browser’s developer tools (F12) or a proxy tool like Burp Suite to intercept and modify web requests.
- Initial Probe: In any user-input field (chat, comment, profile), try submitting benign HTML tags:
<b>test</b>,<i>test</i>,<u>test</u>. - Observe: Submit the message and view the response. Does the word “test” appear bolded, italicized, or underlined? If yes, the application is likely rendering HTML unsafely.
- Bypass Simple Filters: If tags are stripped, try classic bypasses using alternate characters or malformed tags:
<B>test</B>,<b onclick=alert(1)>test</b>, or<<b>script>test</b>.
2. The Payload That Broke Through: ‘ hello
Step‑by‑step guide explaining what this does and how to use it.
The breakthrough came with a minimal, clever payload: a single quote (') followed by a space and then an HTML tag. The researcher discovered that the leading quote and space somehow disrupted the platform’s input sanitization logic, allowing the following content to be interpreted as HTML.
Anatomy and Recreation:
Payload: `’ hello`
The Quote ('): Often used in code to break out of string contexts in poorly constructed backend logic or front-end rendering functions (e.g., element.innerHTML = 'user_input';). The quote might prematurely close a string literal.
The Space: A critical delimiter. It may separate the quote from the following text, preventing it from being seen as part of a single, invalid token, thus allowing the tag to be parsed.
The Tag (<b>): A simple, non-malicious tag to prove rendering occurs. Once `` works, an attacker can escalate to more complex HTML.
Testing Command (Conceptual):
You can simulate this testing logic using `curl` to send various payloads and inspect the HTML in the response.
Replace TARGET_URL and SESSION_COOKIE with your target's details This sends a URL-encoded payload: a single quote, space, and bold tag. curl -X POST 'TARGET_URL' \ -H 'Content-Type: application/x-www-form-urlencoded' \ -b 'SESSION_COOKIE' \ --data 'message=%27+%3Cb%3Ehello%3C%2Fb%3E'
Examine the server’s HTTP response or the resulting page to see if `hello` is present as raw text or if “hello” is visually bold.
- Escalation: Building a Deceptive UI Inside a Chat
Step‑by‑step guide explaining what this does and how to use it.
Proof of concept is one thing; proving impact is another. With HTML injection confirmed, the next step was to build a realistic fake login form. This demonstrates how the vulnerability could be used for phishing or spreading misinformation within a trusted interface.
Crafting the Fake Form:
The researcher injected a more complex HTML payload. Below is a simplified example of what such a payload would look like:
' <div style="background: f0f0f0; padding: 15px; border-radius: 5px; font-family: sans-serif;"> <h3 style="color: 333;">Session Expired</h3> Please re-enter your credentials to continue. <form> <input type="text" placeholder="Username" style="display: block; margin: 10px 0; padding: 8px; width: 200px;"><br> <input type="password" placeholder="Password" style="display: block; margin: 10px 0; padding: 8px; width: 200px;"><br> <button type="submit" style="background: 0073e6; color: white; border: none; padding: 10px 15px; border-radius: 3px;">Login</button> </form> <p style="font-size: 0.8em; color: 666;">This is a security test form.</p> </div>
Key Tactics:
- Inherent Trust: The form appears within the legitimate chat UI, borrowing its inherent trust.
- Social Engineering Text: Using phrases like “Session Expired” creates urgency and legitimacy.
- Basic Styling: Inline CSS makes the form look professional and integrated with the platform. In a real attack, the form could submit data to an attacker-controlled server.
4. Assessing True Impact: The “Shared Chat” Function
Step‑by‑step guide explaining what this does and how to use it.
A vulnerability that only affects the attacker is a low-priority bug. The critical escalation was testing the platform’s “Share Chat” feature. This transformed the finding from “self-injection” into a stored and shareable threat.
Impact Assessment Methodology:
- Create a PoC Chat: In the vulnerable chat, send your HTML injection payload (e.g., the fake form).
- Generate a Share Link: Use the platform’s official “Share” or “Create Link” function.
- Test in a Clean Environment: Open the generated share link in a different browser where you are not logged in, or using an incognito/private window. This simulates how a victim would see it.
- Verify Persistence: Confirm that the injected HTML renders correctly for any user viewing the shared link. This proves the malicious content is stored on the server and served to all viewers, massively increasing its severity.
5. Responsible Disclosure Without a Formal Program
Step‑by‑step guide explaining what this does and how to use it.
Discovering a bug in a platform without a public bug bounty program requires careful, professional communication to avoid legal repercussions and ensure a fix.
Step-by-Step Disclosure Template:
- Gather Evidence: Take clear screenshots and, crucially, record a short video demonstrating the bug from start to finish (e.g., typing the payload, seeing it render, sharing the chat, and viewing it in a private window).
- Find the Right Contact: Look for a `security@` or `abuse@` email on the company’s website, in their privacy policy, or security.txt file (
/.well-known/security.txt).
3. Draft a Clear Report:
Subject: Security Vulnerability Report – HTML Injection in Shared Chats
Body: Briefly describe the issue, its impact (deceptive UI in shared chats), and the steps to reproduce. Explicitly state that you found this during normal product use, did not access other user data, and did not attempt further exploitation.
Attach Evidence: Include your video and screenshots.
Offer Assistance: Propose your availability to answer questions from their engineers.
4. Be Patient and Professional: Allow several business days for a response. Follow up politely if you hear nothing after a week.
What Undercode Say:
Lateral Thinking Over Brute Force: The highest-value security findings often come from creatively pivoting to a less-obvious attack vector when the primary one is well-defended. Persistence in testing subtle variations (like a quote and a space) is key.
Impact is Defined by Context: A bug that seems minor in a private context can become critical when viewed through features like sharing, collaboration, or public profiles. Ethical hackers must always explore how a vulnerability interacts with all application features.
This case is a textbook example of modern bug hunting. It wasn’t a complex buffer overflow or a zero-day, but a clever exploitation of a logic flaw in input sanitization. The researcher’s methodology—probe, pivot, escalate, and contextualize—is replicable across countless web applications. The reward, a 1-year subscription, highlights that companies increasingly value these findings even outside formal bounty programs, as they directly protect user trust and platform integrity.
Prediction:
This incident foreshadows a growing attack surface within collaborative and AI-driven platforms. As features like “shared workspaces,” “public notebooks,” and “collaborative chats” become ubiquitous, vulnerabilities that allow poisoning this shared content will rise in severity. We will see more attacks leveraging HTML/SVG injection and CSS data theft within trusted SaaS interfaces, blurring the lines between client-side bugs and credible phishing threats. Furthermore, the researcher’s tease of an upcoming “rate-limit bypass” points to business logic flaws in AI platforms—such as abusing credit systems, bypassing query limits, or manipulating AI output—becoming the next high-value target for both ethical hackers and malicious actors.
🎯Let’s Practice For Free:
IT/Security Reporter URL:
Reported By: Taher Shabu – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
