CVE-2023-52263

Executive Summary

CVE-2023-52263 is a security advisory affecting Brave Browser versions prior to 1.59.40. The vulnerability lies in the improper restriction of the schema for WebUI factory and redirect, specifically in the files browser/brave_content_browser_client.cc and browser/ui/webui/brave_web_ui_controller_factory.cc. This flaw could allow an attacker to bypass security controls by manipulating WebUI redirects, potentially leading to unauthorized access or information disclosure. The CVSS score is 0.0, indicating that the vulnerability has not been fully assessed or is considered low risk, but the lack of a patch status (UNKNOWN/UNPATCHED) raises concerns. No public exploit or proof-of-concept is available at this time.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a browser-specific issue within the Brave Browser codebase.

CVSS Breakdown & Threat Level

The CVSS score is 0.0, which typically indicates that the vulnerability has not been scored or is considered negligible. However, the advisory suggests a potential security bypass. Without a CVSS vector, the threat level is assessed as Medium due to the possibility of WebUI manipulation, which could lead to privilege escalation or data leakage. The EPSS score of 0.0% indicates a very low probability of exploitation in the wild.

Deep Dive & Mechanics

The vulnerability exists in Brave Browser's WebUI handling. The brave_content_browser_client.cc and brave_web_ui_controller_factory.cc files are responsible for managing WebUI factories and redirects. Improper schema restriction means that an attacker could craft a malicious WebUI URL that bypasses security checks, potentially allowing access to internal browser resources or performing actions with elevated privileges.

The core issue is that the browser does not properly validate the schema (e.g., chrome:// or brave://) for WebUI redirects, allowing an attacker to redirect users to unintended internal pages. This could be exploited via a crafted link or through a compromised website.

Vulnerable vs. Patched Code

Vulnerable Code (pre-1.59.40): The vulnerable code likely lacks proper validation of the WebUI schema during redirects. For example, in brave_web_ui_controller_factory.cc, the factory might accept any schema without checking if it is allowed.

// Vulnerable: No schema validation
bool BraveWebUIControllerFactory::IsWebUIAllowed(const GURL& url) {
  return true; // Always allows
}

Patched Code (1.59.40+): The patched version adds schema validation to ensure only trusted WebUI schemas are allowed.

// Patched: Schema validation added
bool BraveWebUIControllerFactory::IsWebUIAllowed(const GURL& url) {
  if (!url.SchemeIs("chrome") && !url.SchemeIs("brave")) {
    return false; // Reject untrusted schemas
  }
  // Additional checks
  return true;
}

Exploitation & Lab Setup

Red Team

To simulate exploitation, set up a controlled environment with Brave Browser version 1.59.39 or earlier. Create a malicious HTML page that triggers a WebUI redirect:

<!DOCTYPE html>
<html>
<head>
    <title>Exploit PoC</title>
</head>
<body>
    <script>
        // Attempt to redirect to a sensitive WebUI page
        window.location.href = "brave://settings/security";
    </script>
</body>
</html>

Host this page on a local server and trick a user into visiting it. If the vulnerability is present, the browser may allow the redirect without proper validation.

Blue Team

To detect exploitation attempts, monitor for unusual WebUI redirects. Use browser logs or network monitoring to identify requests to brave:// or chrome:// schemas from external sources. Implement Content Security Policy (CSP) headers to restrict WebUI access.

Indicators of Compromise (IOCs)

• URL Patterns: Requests to brave://* or chrome://* from external domains.
• Browser Logs: Entries showing WebUI redirects without proper schema validation.
• Network Traffic: Unusual outbound connections to internal browser resources.

Detection Engineering

YARA Rule

rule CVE_2023_52263_WebUI_Schema_Bypass {
    meta:
        description = "Detects attempts to exploit CVE-2023-52263 via WebUI schema manipulation"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-52263"
    strings:
        $schema_bypass = "brave://" nocase
        $chrome_schema = "chrome://" nocase
    condition:
        any of them
}

Sigma Rule

title: CVE-2023-52263 WebUI Schema Bypass Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit CVE-2023-52263 via WebUI schema manipulation
author: Valters IT
date: 2025-04-10
logsource:
    category: browser
    product: brave
detection:
    selection:
        EventID: 1001
        URL|contains:
            - 'brave://'
            - 'chrome://'
    condition: selection
falsepositives:
    - Legitimate internal WebUI usage
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-52263 WebUI Schema Bypass Attempt"; flow:to_server; content:"brave://"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

1. Update Brave Browser: Upgrade to version 1.59.40 or later to apply the fix.
2. Restrict WebUI Access: Implement Content Security Policy (CSP) headers to block unauthorized WebUI redirects.
3. Monitor Logs: Regularly review browser logs for unusual WebUI activity.
4. User Awareness: Educate users not to click on suspicious links that may trigger WebUI redirects.

Valters IT