CVE-2016-3351

What Is Internet Explorer and Microsoft Edge?

Microsoft Internet Explorer was the dominant Windows browser through the early 2010s and remained widely deployed in enterprise environments due to compatibility with legacy intranet applications. Microsoft Edge (the original EdgeHTML-based version, not the current Chromium-based Edge) was introduced with Windows 10 in 2015 as IE's successor. Both browsers share vulnerability exposure to memory handling flaws in their HTML/DOM rendering engines, JavaScript engines, and component libraries.

Information disclosure vulnerabilities in browsers — while rated lower than code execution bugs — function as critical attack prerequisites. By leaking information about the local filesystem, loaded modules, or memory layout, they allow attackers to break security mitigations (ASLR) and fingerprint victim systems, enabling reliable execution of paired exploitation stages.

Overview

CVE-2016-3351 is an information disclosure vulnerability in Internet Explorer and Microsoft Edge that allows an attacker to determine whether specific files exist on the victim's computer. A remote attacker who persuades a user to visit a malicious web page can use JavaScript interactions with browser memory objects to infer local file presence. The ransomwareUse: true flag reflects CISA's confirmation that this information disclosure was integrated into ransomware delivery chains — exploit kits used it to fingerprint victim systems and enable ASLR bypass before delivering ransomware payloads. Patched in MS16-104 (Internet Explorer) and MS16-105 (Edge) on September 13, 2016. CISA added CVE-2016-3351 to the KEV catalog in May 2022.

Affected Versions

Technical Details

Root Cause: Memory Object Handling Information Leak

CVE-2016-3351 is an information disclosure vulnerability (CWE-200) in the way Internet Explorer and Edge handle certain objects in memory. When browser JavaScript or HTML content interacts with specific browser APIs, the browser's internal handling of those objects may leak information about the local filesystem — specifically whether particular file paths exist on the victim's machine.

The mechanism exploits subtle differences in browser behavior (timing, error messages, or return values) when file paths are referenced through browser APIs:

• When a referenced path exists, the browser may behave differently (response time, DOM state change, error type)
• When the path does not exist, a different code path triggers
• By comparing these behavioral differences across many file paths, an attacker can enumerate which files are present

File Detection Attack Surface

Knowing which files exist on a victim's system provides an attacker with:

• Antivirus/EDR product identification: Check for vendor-specific DLL or executable paths (C:\Program Files\<AV vendor>\) to identify installed security products and select appropriate evasion
• Software version fingerprinting: Presence or absence of version-specific files (patch artifacts, version-specific executables) reveals which patches are installed
• Browser and Office version confirmation: Confirm which specific version of IE/Office/Windows the victim is running to choose the correct exploit variant
• ASLR bypass via module enumeration: In some exploitation contexts, confirming which DLLs are loaded at which filesystem paths correlates with memory layout, helping defeat ASLR

Ransomware Exploit Chain Integration

CVE-2016-3351 was integrated into exploit kit operations targeting ransomware delivery:

1. Victim visits malicious page in IE or Edge
2. File detection stage — JavaScript exploits CVE-2016-3351 to fingerprint the victim's security software and OS version
3. Exploit selection — the exploit kit selects the appropriate browser RCE exploit for the confirmed configuration
4. ASLR bypass — disclosed file/module information assists in targeting memory addresses for the RCE stage
5. Ransomware delivery — the RCE stage drops and executes the ransomware payload

Attack Characteristics

Discovery

Identified through Microsoft security research; patched in September 2016 Patch Tuesday security updates for both Internet Explorer (MS16-104) and Edge (MS16-105).

Exploitation Context

• Exploit kit integration: Exploit kits including RIG, Neutrino, and Magnitude integrated file detection information disclosure vulnerabilities as reconnaissance components in their exploitation chains throughout 2016; CVE-2016-3351 was a September 2016 addition to this capability
• Paired with browser RCE: Information disclosure vulnerabilities are rarely used in isolation; CVE-2016-3351 provided system fingerprinting and ASLR bypass support for paired IE/Edge memory corruption exploits in the same exploit kit flow
• CISA ransomwareUse designation: CISA's confirmation of ransomware use reflects that the exploit kits using CVE-2016-3351 ultimately delivered ransomware families (Locky, CryptoMix, Cerber) as their primary payload during this period
• Affects both IE and Edge: The vulnerability's presence in both legacy IE and the newer Edge browser widened the exposure; Windows 10 users on Edge were not automatically safer than Windows 7 IE users from this specific vulnerability
• CISA KEV (2022): Added May 2022, reflecting continued tracking of this vulnerability's historical exploitation in ransomware delivery infrastructure

Remediation

1. Apply MS16-104 and MS16-105 — install the September 2016 cumulative security updates for Internet Explorer and Edge respectively. All subsequent cumulative IE and Windows updates include these fixes.

2. Migrate from Internet Explorer to Microsoft Edge — Microsoft ended support for IE 11 on June 15, 2022 (except on Windows Server). Migrate users to Chromium-based Edge, which provides significantly stronger security architecture and active security support.

3. Upgrade from legacy Windows versions — Windows 7 and Server 2008 R2 are end-of-life; IE on those systems receives no further patches. Migrate to Windows 10/11.

4. Apply monthly cumulative updates — maintain monthly Windows Update cadence to receive all browser and OS security fixes promptly; exploit kits specifically target the gap between patch release and deployment.

5. Deploy browser isolation or NG-WAF — consider browser isolation technology or next-generation web filtering that can prevent malicious JavaScript execution against known exploit kit infrastructure.