CVE-2025-53599: 
Homebrew vulnerability analysis and mitigation

CVE-2025-53599 is a Cross-Site Scripting (XSS) vulnerability in NAVER's Whale browser for iOS that allows attackers to execute malicious scripts in the browser via a crafted JavaScript scheme. It affects all versions of Whale browser for iOS prior to 3.9.1.4206. The vulnerability was published on July 4, 2025, and assigned by NAVER. It carries a CVSS v3.1 base score of 9.8 (Critical) (Red Hat CVE, NAVER CVE).

The vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation — Cross-Site Scripting), rooted in insufficient validation or sanitization of JavaScript scheme URIs processed by the Whale iOS browser. An attacker can craft a malicious javascript: scheme URL that, when processed by the browser, bypasses input controls and triggers arbitrary script execution within the browser's context. No authentication or user interaction is required, and the attack is network-accessible, making it remotely exploitable without preconditions. Relevant CAPEC patterns include DOM-Based XSS (CAPEC-588), Reflected XSS (CAPEC-591), and Stored XSS (CAPEC-592) (NAVER CVE, Red Hat CVE).

Successful exploitation allows an attacker to execute arbitrary JavaScript within the Whale iOS browser context, potentially compromising user session data, stealing sensitive information (e.g., cookies, credentials), performing actions on behalf of the user without consent, and injecting malicious content into browser sessions. The CVSS score reflects high impacts to confidentiality, integrity, and availability, indicating the potential for significant data exposure and browser compromise (Red Hat CVE, NAVER CVE).

As of the time of disclosure, there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation (Red Hat CVE). The EPSS score is approximately 0.029%, indicating a low current probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported.

1. Reconnaissance: Identify iOS users running NAVER Whale browser versions prior to 3.9.1.4206, potentially via social engineering, phishing campaigns, or targeting known Whale browser user communities.
2. Craft malicious payload: Construct a URL or web page containing a crafted javascript: scheme URI designed to bypass Whale browser's input handling (e.g., javascript:alert(document.cookie) or a more sophisticated payload for session hijacking).
3. Deliver payload: Distribute the crafted link via phishing email, SMS, malicious QR code, or embed it in a web page that the target is likely to visit on their iOS device.
4. Trigger execution: When the victim opens the crafted link in Whale browser for iOS, the malicious JavaScript executes within the browser context without any additional user interaction.
5. Achieve objective: Exfiltrate session cookies, credentials, or other sensitive data to an attacker-controlled server, or perform unauthorized actions within the browser session (NAVER CVE).

• Network: Outbound HTTP/HTTPS requests from the iOS device to unexpected or unknown external servers shortly after opening a suspicious link in Whale browser; unusual DNS queries to attacker-controlled domains.
• Logs: Browser access logs (if available) showing navigation to URLs containing javascript: scheme patterns with encoded or obfuscated payloads.
• Behavioral: Unexpected browser behavior such as unsolicited redirects, pop-ups, or form submissions; session tokens appearing in external network traffic not initiated by the user.

Users should immediately update NAVER Whale browser for iOS to version 3.9.1.4206 or later, which contains the fix for this vulnerability (NAVER CVE). As interim mitigations, administrators and users should avoid clicking on untrusted links, and organizations can implement Content Security Policy (CSP) on web properties to restrict script execution. Monitoring for suspicious JavaScript activity and educating users about browser-based phishing attacks are also recommended defensive measures.