CVE-2017-18256 in Brave Browser
Summary
by MITRE
Brave Browser before 0.13.0 allows remote attackers to cause a denial of service (resource consumption) via a long alert() argument in JavaScript code, because window dialogs are mishandled.
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Analysis
by VulDB Data Team • 12/03/2025
The vulnerability identified as CVE-2017-18256 represents a significant resource consumption issue within the Brave Browser version 0.13.0 and earlier. This flaw stems from the improper handling of window dialogs, specifically when JavaScript code executes alert() functions with excessively long arguments. The vulnerability falls under the category of denial of service attacks, where malicious actors can exploit this weakness to consume system resources and potentially render the browser unresponsive or crash it entirely. The issue demonstrates a critical gap in input validation and resource management within the browser's JavaScript execution environment.
The technical implementation of this vulnerability exploits the browser's dialog handling mechanism by passing extremely long strings as arguments to the alert() function. When the browser attempts to display this oversized dialog box, it consumes disproportionate amounts of memory and processing power. The flaw occurs because the browser fails to implement proper bounds checking or resource limits when processing these dialog arguments, allowing attackers to craft malicious JavaScript code that repeatedly triggers this behavior. This type of vulnerability is classified under CWE-400 as "Uncontrolled Resource Consumption" and represents a classic example of a resource exhaustion attack pattern.
From an operational perspective, this vulnerability poses substantial risks to users who may inadvertently encounter malicious web content or be targeted by phishing attacks that leverage this specific weakness. The denial of service impact can be severe, as it affects the browser's ability to function normally and can potentially be used to disrupt user productivity or as part of larger attack campaigns. The vulnerability is particularly concerning because it can be exploited through standard web browsing activities without requiring any special privileges or user interaction beyond visiting a malicious website. Attackers can craft JavaScript payloads that automatically trigger multiple alert() calls with large arguments, causing the browser to consume increasing amounts of memory until system resources are exhausted.
The mitigation strategies for this vulnerability primarily involve updating to Brave Browser version 0.13.0 or later, where the issue has been addressed through improved input validation and resource management. Security administrators should implement browser update policies that ensure all users maintain current versions of their browsers. Additionally, organizations can deploy content security policies and web application firewalls to detect and block malicious JavaScript payloads that attempt to exploit this vulnerability. The fix typically involves implementing proper bounds checking for dialog arguments and establishing resource limits to prevent excessive memory allocation during dialog display operations. This remediation aligns with ATT&CK technique T1499.004 for "Resource Hijacking" and demonstrates the importance of proper input validation in preventing resource exhaustion attacks. Organizations should also consider implementing browser hardening measures and monitoring for unusual resource consumption patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of robust input validation and resource management in browser security implementations, particularly when handling user-supplied content.