CVE-2014-4123

What Is Internet Explorer's Zone Security Model?

Internet Explorer implements a zone-based security model that assigns content to security zones (Internet, Local Intranet, Trusted Sites, Restricted Sites) with different privilege levels. Combined with Protected Mode (low-integrity process sandbox), IE's security architecture is designed to prevent web content from accessing OS resources or escalating privileges. Privilege escalation vulnerabilities — which allow content from a restricted zone or a low-integrity process to gain capabilities of a higher zone or integrity level — are sandbox escapes that break this security model.

Overview

CVE-2014-4123 is a privilege escalation vulnerability in Internet Explorer that allows a remote attacker, via a crafted web site, to gain elevated privileges beyond those of the normal IE sandbox. Like CVE-2014-2817 (MS14-051, August 2014), this vulnerability functions as the second-stage component in a browser exploit chain — following an initial remote code execution vulnerability that gives code execution inside IE's Protected Mode. Patched in MS14-056 (October 14, 2014).

Affected Versions

Fixed in MS14-056 (October 2014 cumulative IE update).

Technical Details

Root Cause: Improper Zone/Integrity Enforcement

CVE-2014-4123 involves a flaw in how IE enforces security boundaries between zones or integrity levels. The vulnerability allows content operating under IE's restricted security context (Protected Mode or Internet Zone) to trigger a code path that bypasses the integrity check, performing actions at a higher privilege level.

The exploitation typically occurs as part of a two-stage chain:

1. RCE exploit: An IE memory corruption vulnerability achieves code execution inside the low-integrity Protected Mode process
2. CVE-2014-4123: The compromised sandbox process triggers the zone elevation bug to escape from Protected Mode, gaining medium-integrity (user-level) code execution

This pattern mirrors other IE sandbox escapes (CVE-2014-2817, CVE-2014-0546) and represents the standard approach to complete browser-based exploitation: remote code execution → sandbox escape → full user-level access.

Attack Characteristics

Discovery

Reported to Microsoft and included in the October 2014 cumulative Internet Explorer security update (MS14-056), which addressed multiple memory corruption and privilege escalation vulnerabilities.

Exploitation Context

• Exploit chain component: Used in conjunction with IE RCE vulnerabilities by APT groups and exploit kit operators to achieve full OS-level compromise via browser
• Exploit kit integration: October 2014 IE vulnerabilities were rapidly integrated into commercial exploit kits (Angler, Nuclear) for mass criminal exploitation
• CISA KEV (2022): Added May 2022, reflecting continued exploitation of the full IE vulnerability class against unpatched legacy deployments

Remediation

1. Apply MS14-056 (October 2014 cumulative IE update).

2. Retire Internet Explorer — Microsoft ended support June 15, 2022. No further patches exist for any IE vulnerability. Migrate to Microsoft Edge (Chromium) or another supported browser.

3. Enable Enhanced Protected Mode (EPM) for IE 10/11 to strengthen the sandbox against these elevation attacks.

4. Block IE execution via AppLocker or Windows Defender Application Control if migration cannot be completed immediately.