Address Bar Spoofing in Contemporary Web Browsers: A Taxonomy, Exploitation Study, and Mitigation Guidelines

Renua Hiwa Ismael, Jaza Mahmood Abdullah

Department of Information Technology, College of Commerce, University of Sulaimani, Sulaymaniyah, Iraq

Corresponding author’s e-mail: Renua Hiwa Ismael, Department of Information Technology, College of Commerce, University of Sulaimani, Sulaymaniyah, Iraq. E-mail: renwax23@gmail.com
Received: 12-07-2025 Accepted: 25-09-2025 Published: 30-11-2025

DOI: 10.21928/uhdjst.v9n2y2025.pp335-345



ABSTRACT

The browser address bar is the cornerstone of user trust and web security. Despite advancements, address bar spoofing remains a persistent threat, enabling attackers to make malicious URLs appear legitimate. This paper presents an extensive investigation into address bar spoofing vulnerabilities across modern desktop and mobile browsers. We introduce a comprehensive taxonomy classifying over 15 distinct spoofing techniques, many of which are novel. Across systematic testing, over 70 vulnerabilities were identified and responsibly disclosed, resulting in patches across more than 15 browsers. These findings are enumerated in this paper for verification. This research analyzes the root causes of these vulnerabilities, highlighting common pitfalls in URL parsing, display logic, and UI state management. Based on our findings, we propose a robust mitigation framework and best practices for browser developers, alongside actionable advice for users. Our findings underscore the ongoing challenge of maintaining address bar integrity and the critical need for continuous vigilance in browser security. A public repository documents these findings to aid further research.

Index Terms: Address Bar Spoofing, Web Browser Security, Phishing, URL Spoofing, UI Security, Vulnerability Taxonomy, Cyber Security

1. INTRODUCTION

Phishing attacks continue to be one of the most prevalent and damaging cyber threats, costing individuals and organizations billions of dollars annually [1]. Attackers employ various social engineering tactics, often relying on deceptive URLs to trick victims. While URL masking or cloaking techniques are common, a more insidious form of deception is address bar spoofing, where a vulnerability within the web browser itself is exploited to display a trusted origin (e.g., bank.com) while the user is actually interacting with a malicious site. This undermines the fundamental trust users place in the address bar as an authenticator of web identity [2].

Despite significant efforts by browser vendors to harden this critical UI component, our research demonstrates that address bar spoofing is not a solved problem. Modern browsers, with their complex feature sets and support for diverse URI schemes and UI states, introduce new attack surfaces. This paper details an extensive, multi-year investigation into these vulnerabilities across prevalent desktop (Windows, macOS) and mobile (iOS, Android) browsers, including Chrome, Firefox, Safari, Edge, Opera, Brave, Arc, and others.

A comprehensive dataset, including detailed descriptions, Proof-of-Concept (PoC) code, and replication videos for all 74 vulnerabilities discussed, is publicly available in our repository [3]. For direct verifiability within this paper, a summary of these findings is provided in Appendix A.

The primary contributions of this paper are:

  1. Demonstrated Persistence and Novelty: We uncovered over 70 distinct address bar spoofing vulnerabilities, many leveraging novel or refined exploitation techniques, leading to direct security improvements in over 15 browsers.

  2. Comprehensive Vulnerability Taxonomy: We developed a structured taxonomy classifying diverse spoofing techniques, moving beyond isolated bug reports to provide a systematic understanding of the attack surface.

  3. Actionable Mitigation Framework: Based on identified root causes, we propose concrete mitigation strategies for browser developers and user education guidelines.

2. THE EVOLVING THREAT OF ADDRESS BAR SPOOFING

Address bar spoofing is not a new phenomenon. Chromium’s guidelines for URL display [4] acknowledge many such scenarios. Early instances date back to vulnerabilities in browsers, such as Internet Explorer 6, exploiting dialog boxes or character encoding quirks [5]. Over time, attacks evolved to leverage weaknesses in handling HTTPS indicators with delayed responses [6], Unicode homograph attacks [7], race conditions in mobile browsers [8], manual spoofing tests [9], and flawed server-side redirect handling [10]. However, as browsers add new features (e.g., Picture-in-Picture, varied URI scheme support) and UIs evolve, new vectors for spoofing continually emerge, often due to subtle implementation errors or incomplete parsing and validation logic. Our research found that even browsers built on mature, security-focused engines, such as Chromium and Gecko are susceptible to these attacks when specific UI choices or feature integrations are made.

3. RESEARCH METHODOLOGY

Our research methodology involved a multi-staged approach conducted over a multi-year period (2019–2024). This section details our testing environment and the systematic process used for vulnerability discovery, analysis, and classification.

3.1. Threat Model and Assumptions

For this research, we assume a standard web-based threat model. The attacker is capable of hosting a malicious website and can persuade a victim to click a link leading to it (e.g., through a phishing email or social media message). However, the attacker cannot install malware on the victim’s machine or compromise the underlying operating system. The victim is assumed to be a non-expert user who relies on the browser’s UI, particularly the address bar, as a primary indicator of a website’s identity. The goal of the attacker is to exploit a browser vulnerability to make their malicious site’s address appear as a trusted, legitimate domain.

3.2. Testing Environment and Scope

Our investigation targeted a wide range of modern web browsers across major desktop and mobile platforms. We primarily focused on the latest stable and beta versions available during the testing periods to ensure relevance. The scope of our test environment is summarized in Table 1.

TABLE 1: Overview of the testing environment and scope

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3.3. Analysis Stages

Our process consisted of five distinct stages:

  1. Systematic Testing of Browser Features: We systematically tested browser features known to be complex or historically problematic. For each feature, we developed a test plan to probe edge cases. For instance, to test data: URI handling, over 50 permutations were crafted, varying the encoding, position of hostname-like strings, and special characters to observe parsing and display logic. Features tested included search engine integration, Address bar freezing, internal URI schemes, full screen/PiP APIs, blob/data/javascript URI schemes, RTL character display, and Unicode parsing.

  2. Reverse-Engineering Browser Behavior: For identified anomalies, we analyzed browser behavior to determine the root cause. This sometimes-involved decompiling Android applications or examining open-source code. For example, to diagnose a search query spoof in Opera Mini (ID: 11), we used jadx-gui [11] to decompile the Android application package (APK). By analyzing the Java class responsible for parsing search provider URLs, we identified a flawed regular expression that failed to correctly validate the origin.

  3. Exploitation and PoC Development: Once a potential vulnerability was identified, we developed a minimal PoC to confirm its exploitability and demonstrate its security impact.

  4. Responsible Disclosure: All vulnerabilities were reported to the respective browser vendors through bug bounty programs (e.g., HackerOne, Bugcrowd) or direct security contacts. Public disclosure of details was withheld until patches were made available or a reasonable timeframe had passed.

  5. Taxonomy Creation: Based on the diverse attack vectors and root causes, we categorized all confirmed vulnerabilities into the comprehensive taxonomy presented in Section 4.

4. A COMPREHENSIVE TAXONOMY OF ADDRESS BAR SPOOFING TECHNIQUES

Our research identified numerous ways attackers can manipulate the browser’s address bar. The following taxonomy categorizes the primary techniques observed. For brevity, only a selection of categories and illustrative examples are presented.

To provide a more structured overview, Table 2 summarizes the key characteristics of the primary spoofing classes identified in our research, including their typical root cause and user interaction requirements.

TABLE 2: Characteristics of spoofing technique classes

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4.1. UI State Manipulation

Exploiting browser states like Full-screen mode or features, such as Picture-in-Picture (PiP) to obscure or replace the authentic address bar.

  • Full-screen Spoofing: An attacker’s site requests full-screen mode upon user interaction. The browser UI, including the address bar, disappears. The attacker then renders a fake address bar image within the web content, tricking the user (Fig. 1). While some browsers warn upon entering full screen, many do not, or the warning is easily missed.

  • Window without Address Bar (e.g., via PiP): Certain APIs, such as Picture-in-Picture, can create new windows or views without a native address bar. Attackers can then draw a fake address bar within this content area. We found Microsoft Edge on Mac vulnerable to this via PiP.

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Fig. 1. Demonstration of Fullscreen Spoofing in Opera Mobile. (Left) The attacker’s page (attacker.com) enters fullscreen, hides the real UI, and renders a fake address bar image showing opera.com. (Right) The legitimate opera.com site shown in the standard browser view for comparison.

4.2. Non-Standard Scheme Handling

Abusing the browser’s often less-rigorous parsing, validation, and display logic for URIs beyond standard http and https.

  • Data: URI Spoofing: data: URIs embed content directly. We found that by crafting a data: URI with a spoofed hostname-like string before the actual comma-separated data (e.g., data://google.com/,<malicious_content>), some mobile browsers (such as Arc Mac or Opera GX Android) would misleadingly display google.com in the address bar. See Fig. 2 for an example in Arc Mac.

  • Blob: URI Spoofing: blob: URIs represent raw data. Some browsers, when navigating to a blob: URI, display the full blob URL. By appending a hash fragment containing the spoofed URL (e.g., blob: https://real-origin.com/GUID#https://spoofed.com), browsers, such as Safari would prioritize displaying the fragment, effectively hiding the true blob: origin.

  • JavaScript: URI Spoofing: Redirecting to or opening a JavaScript: URI can lead to confusion. In PlayStation 5’s browser, redirecting to a legitimate site, then immediately opening a new window to a JavaScript: URI caused the address bar to retain the legitimate site’s URL while executing an attacker-controlled script that wrote to the new window.

  • Internal URI Schemes: Browsers use internal schemes (e.g., internal://, arcmobile-internal://) for error pages or special functions. Redirecting to these schemes, often with parameters controlling the displayed URL, allowed spoofing. For example, Firefox for iOS allowed redirection to internal://local/errorpage?url=https://google.com/., which would display google.com while allowing content.

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Fig. 2. Exploitation of data: URI parsing in Arc for macOS. The address bar misleadingly displays google.com, a string parsed from the URI path while the page content is fully controlled by the attacker via the data: URI itself.

4.3. Navigation Timing and Race Conditions

Capitalizing on the temporal gap between initiating a navigation request and receiving a definitive server response.

  • URL Freeze (Change Before Response): The most common vulnerability. An attacker redirects to an unreachable port on a legitimate domain (e.g., google.com:8081). Many browsers immediately update the address bar to google.com before realizing the port is unreachable. The page content remains attacker-controlled, leading to a spoof (Fig. 3). This was observed in numerous browsers, including Arc Android and Safari.

  • HTTP 204 No Content: This technique is distinct from URL Freeze: while URL Freeze exploits an unreachable destination, the HTTP 204 attack uses a valid but empty server response. The browser correctly updates the address bar to the target URL, but because no new content is sent, the attacker’s original page content remains visible. This was observed in Arc for Android.

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Fig. 3. Flowchart of a “URL Freeze” timing attack. The browser pre-maturely updates the address bar to a legitimate domain (bing.com) upon redirection, but the destination port is unreachable, causing the navigation to fail while leaving the spoofed address and attacker-controlled content visible.

4.4. URL Parsing and Display Logic Flaws

Leveraging ambiguities in how browsers parse, truncate, and display complex URLs.

  • Long Domain/Subdomain to Hide Origin: On small screens (especially mobile), long subdomains (e.g., very.long.subdomain.target.com.attacker.com) can cause the browser to truncate the URL, potentially only showing very.long.subdomain.target.com and hiding attacker.com. Firefox for Android/iOS was vulnerable, prioritizing the beginning of the URL, PoC in Fig. 4.

  • Search Engine Integration Quirks: Some mobile browsers display the search query in the address bar instead of the search engine’s URL. Flaws in validating the search engine’s origin or path allowed spoofing. For example, a malformed regex in Opera GX allowed google.pwn.wtf to be treated as a Google search, displaying the query from ?q= as the URL. The Arc browser for iOS was similarly vulnerable.

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Fig. 4. Long Subdomain Spoof in Firefox Mobile. The browser truncates the long URL, prioritizing the display of the fake subdomain (accounts.login.google.com…) while completely hiding the true, malicious origin (…github.io).

4.5. Unicode and Right-to-Left (RTL) Manipulation

Utilizing visually confusable Unicode characters or exploiting complex rendering rules for mixed RTL/LTR text.

  • Unicode Whitespace-like Characters: Characters like U+08FC can appear as whitespace. Bentkowski [12] showed this could be used in domains, such as important-domain.google.com<U+08FC><U+08FC>evil.com, where Chrome/Firefox would display only the important-domain.google.com part.

  • RTL/LTR Confusion: Mixing RTL (e.g., Arabic, Kurdish) and LTR (e.g., English) scripts in a domain can confuse the browser’s display logic, causing parts of the URL to be reordered or hidden, leading to spoofing. Brave for iOS was vulnerable when displaying domains like https://xn--llb.login.accounts.google.com.xn--llb.attacker.com, misrendering the true origin.

4.6. Browser Internal Component Interaction

Exploiting vulnerabilities within or between privileged browser components.

  • Internal Pages XSS: An XSS in a privileged internal browser page (e.g., arcmobile-internal://in Arc iOS) responsible for rendering UI elements or handling errors could be used to manipulate the address bar display by controlling parameters passed to this internal URI.

5. RESULTS AND DISCUSSION

Our process involved identifying and classifying each vulnerability, reporting it to the vendor for patching, documenting the entire procedure along with the root causes that are shared among them, and then assigning severity ratings of each spoof.

5.1. Statistical Overview

Our research initiated in 2019 and intensified recently, uncovered over 70 unique address bar spoofing vulnerabilities across 15+ different web browsers and browser-based applications on various platforms. This led to over $80,000 in bug bounty reward. Table 3 summarizes the number of unique vulnerabilities found in selected major browsers (mobile versions included).

TABLE 3: Number of vulnerabilities found in major web browser vendors

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TABLE 4: Severity Scoring Rubric for Address Bar Spoofing

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5.2. Key Root Causes

Several recurring themes emerged as root causes:

  1. Premature Address Bar Update: Changing the address bar value before navigation is complete and a response is received (most common), URL freezing and navigation timing.

  2. Window/View Without Address Bar: Features creating content views (PiP, certain extension APIs) without mandating a secure, native address bar.

  3. Flawed URL Truncation/Display Logic: Incorrectly prioritizing the beginning/end of long URLs or failing to clearly indicate the true registrable domain.

  4. Insufficient Prompts/Notifications: Lack of clear user notification when entering states, such as full screen, where the address bar is hidden.

  5. Insecure Handling of Search Engine Queries: Weak validation of search engine origins/paths when displaying queries in the address bar.

  6. Lax Parsing of Non-HTTP(S) Schemes: Treating schemes, such as data:, blob:, or internal URIs, with less rigor than http(s), leading to misinterpretation of origin.

  7. Incorrect RTL/Unicode Character Handling: Failure to correctly parse and display mixed-direction text or confusable Unicode characters in domain names.

5.3. Exploitability and Severity

Vulnerabilities ranged in severity:

To move beyond qualitative descriptions, we developed a bespoke scoring rubric to consistently assess the severity of each vulnerability. This framework, summarized in Table 4, was inspired by CVSS but adapted for UI spoofing, scores vulnerabilities on two primary factors: Visual Fidelity and Interaction Complexity.

Severity is assigned based on the sum of the two scores (ranging from 2 to 6):

  • High severity (Score 5–6): These vulnerabilities achieve near-perfect mimicry with minimal or no user interaction. They pose the most significant threat. Example: The Safari about: blank spoof (Fig. 5) was pixel-perfect (Score 3) and required a single click (Score 2), for a total score of 5.

  • Medium severity (Score 3–4): These spoofs are convincing but have minor visual flaws or require more obvious user interaction. Example: The Brave iOS blob: URI spoof required one click (Score 2) but had minor visual inconsistencies (Score 2), for a total score of 4.

  • Low severity (Score 2): These attacks are less realistic, rely on uncommon browser states, or require significant user interaction, making them less likely to succeed. Example: The Opera GX Unicode freeze required specific text selection (Score 1) and was visually flawed (Score 1), for a total score of 2.

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Fig. 5. High-Severity Spoof in Safari. A comparison shows an attacker-controlled page rendering a fake address bar (bottom) that is pixel-perfect and visually indistinguishable from the legitimate browser UI (top), demonstrating a highly convincing attack.

Browsers, such as Opera and Arc, which implement many new features and adjust the address bar more toward UX and esthetic look, are more prone to spoofing attacks, even “imperfect” spoofs pose a real risk to unsuspecting users. Responsible disclosure timelines varied, with some vendors patching within days and others taking several months.

6. MITIGATION STRATEGIES

A multi-layered approach is necessary to effectively mitigate address bar spoofing, along with the browser vendor and user knowledge in the area.

6.1. Proposed Fixes and Recommendations for Browsers

  1. Always Show Top-Level Domain Clearly:

    • If a URL is too long, prioritize displaying the TLD and the end of the URL path. Do not hide the TLD.

    • For multiple subdomains, ensure the registrable domain (e.g., example.com in sub.example.com) is always visible and clearly distinguished (Fig. 6).

  2. Don’t Change Address Value Before Response: Only update the address bar after a successful response from the destination server is received and content begins to render. For unreachable destinations or HTTP 204, either revert to the previous URL or clear content and display the new URL with an empty/error page (Fig. 7).

  3. Show Prompts for UI State Changes: Clearly notify users when entering states, such as full-screen or landscape mode if the address bar is hidden.

  4. Address Bar is for URLs, Not Search Queries: Ideally, always display the search engine’s URL. If queries must be shown, use robust origin/path validation for the search engine.

  5. Don’t Expose Internal URIs to Web Pages: Prevent web content from redirecting to or interacting with privileged internal browser URIs.

  6. Every Window Must Have a Secure Address Bar: All windows/tabs/popups/PiP displaying web content must have a non-spoofable, browser-controlled address bar displaying the present origin.

  7. Correctly Parse and Display Non-HTTP Schemes: For about: blank, blob:, data:, etc., clearly indicate the scheme and its nature (e.g., “insecure,” “local data:”, “blob:” URI). Do not allow hash fragments to obscure the scheme itself.

  8. Correctly Display RTL Domains: Implement strict parsing and display rules for mixed RTL/LTR domains to prevent visual reordering that hides the true origin.

  9. Maintain the “Line of Death”: Strictly enforce separation between browser chrome (trusted UI) and web content. Prevent web content from overlaying or interacting with the address bar area, a principle core to Browsers and Applications’ security UI design [13].

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Fig. 6. Diagram illustrating the correct principle for displaying long URLs. The browser UI must always prioritize displaying the true registrable domain (attacker.com) rather than potentially deceptive subdomains, which can be arbitrarily long.

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Fig. 7. Flowchart for a secure address bar update process. The UI should only change the displayed origin after receiving a successful response from the destination server, preventing timing attacks where the navigation fails.

6.2. User Education

  1. Type Sensitive Addresses Manually or Use Trusted Bookmarks: Especially for banking or critical services.

  2. Use Developer Tools to Verify Origin: In case of suspicion, console.log (location.origin) reveals the true origin or Inspect site identity via browser padlock icon/certificate details.

  3. Keep Browsers Updated: Apply security patches promptly.

  4. Be Wary of Unexpected Behavior: If a site looks slightly off or behaves unusually after clicking a link, exercise caution.

7. DISCUSSION AND CONCLUSION

This research has systematically demonstrated that address bar spoofing remains a significant and evolving threat in contemporary web browsers. By developing a comprehensive taxonomy, discovering and disclosing over 70 vulnerabilities, and analyzing their root causes, we have provided a deep insight into the present state of address bar security.

Our analysis of the findings in Table 3 reveals notable trends. Chromium-based browsers that implement heavy UI customizations, such as Opera, Opera GX, and Arc, accounted for a disproportionately high number of vulnerabilities. These often stemmed from unique features, such as custom search engine integrations or non-standard UI state handling, suggesting that deviations from the core Chromium security model introduce new attack surfaces. In contrast, vulnerabilities in WebKit (Safari) were more frequently tied to the nuanced handling of non-standard URI schemes, such as blob:, while Gecko (Firefox) showed susceptibility to URL truncation on mobile displays. This highlights that while engine-level security is mature, browser-specific feature implementations remain a primary source of spoofing vulnerabilities.

The findings underscore a persistent between usability and security. Features designed to create a cleaner UX – such as fast address bar updates, hiding URL components, and novel UI states, such as Picture-in-Picture – are frequently the source of the security flaws we identified. While this research was extensive, it could not cover every browser or operating system, and niche browsers may harbor similar flaws.

In conclusion, maintaining the integrity of the address bar requires continuous, meticulous attention to detail across navigation logic, protocol handling, and UI rendering. Our proposed mitigation strategies offer a multi-layered defense to help vendors fortify this critical UI element. For future work, we recommend two key directions: (1) Expanding testing to include embedded web views and browser extensions, which represent growing attack surfaces, and (2) developing standardized, automated testing tools to systematically probe for these complex UI-based vulnerabilities at scale. The insights from this research aim to significantly advance the understanding and fortification of this crucial element of web security, ultimately working toward a safer online experience.

REFERENCES

[1] StationX, “Phishing Statistics“, 2024. Available from:https://www.stationx.net/phishing-statistics [Last accessed on 2025 Jul 10].

[2] “Trend Micro. Address Bar Spoofing.“Available from:https://www.trendmicro.com/vinfo/us/security/definition/address-bar-spoofing [Last accessed on 2025 Jul 10].

[3] R. Ismael. “Address Bar Spoofing. GitHub Repository,“2025. Available from:https://github.com/renwax23/address_bar_spoofing [Last accessed on 2025 Jul 10].

[4] Chromium. “Guidelines for URL Display.“Available from:https://chromium.googlesource.com/chromium/src/+/HEAD/docs/security/url_display_guidelines/url_display_guidelines.md [Last accessed on 2025 Jul 10].

[5] Y. Koster. “Address Bar Spoofing flaw in Internet Explorer,“ 2004. Available from:https://www.akitasecurity.nl/advisory/AK20040801/address_bar_spoofing_flaw_in_internet_explorer.html [Last accessed on 2025 Jul 10].

[6] L. Treiber. “Google Chrome HTTPS Address Bar Spoofing,“2012. Available from:https://blog.acrossecurity.com/2012/01/google-chrome-https-address-bar.html [Last accessed on 2025 Jul 10].

[7] C. Weber. “Unicode Security Guide - Visual Spoofing,“2014. Available from:https://cweb.github.io/unicode-security-guide/visual-spoofing

[8] R. Baloch. “Bypassing Mobile Browser Security for Fun and Profit. In:Presented at BlackHat Asia,“2016.

[9] “Chromium. Chromium Trickuri GitHub Repo,“2019. Available from:https://github.com/chromium/trickuri [Last accessed on 2025 Jul 10].

[10] R. Baloch. “Multiple Address Bar Spoofing Vulnerabilities in Mobile Browsers,“ 2020. Available from:https://www.rafaybaloch.com/2020/10/multiple-address-bar-spoofing-vulnerabilities.html

[11] Skylot, “Jadx GitHub Repo.“Available from:https://github.com/skylot/jadx [Last accessed on 2025 Jul 10].

[12] M. Bentkowski. Address Bar Spoofing in Chrome and Firefox, 2017. Available from:https://research.securitum.com/address-bar-spoofing-in-chrome-and-firefox-description-of-cve-2017-5089-and-cve-2017-7763 [Last accessed on 2025 Jul 10].

[13] E. Law. “The Line of Death,“2017. Available from:https://textslashplain.com/2017/01/14/the-line-of-death [Last accessed on 2025 Jul 10].

[14] A. N. Joinson, U. D. Reips, T. Buchanan and C. B. P. Schofield. “Privacy, trust, and self-disclosure online.“Human-Computer Interaction, vol. 25, no. 1, pp. 1-24, 2010.

[15] K. Yee. “Aligning security and usability.“IEEE Security and Privacy, vol. 2, no. 5, pp. 85-88, 2004.

APPENDIX A: SUMMARY OF DISCLOSED VULNERABILITIES

The following table summarizes the 74 unique vulnerabilities identified and disclosed during this research. The full dataset, including PoC codes, image/video PoCs, bounty amount, timeline and full bug description, is available at the repository cited in Ismael [3]. The “Taxonomy Class” refers to the categories defined in Section 4. Note: Not all browsers assign CVEs, which is why some are missing.

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