Microsoft Internet Explorer Information Disclosure Vulnerability September 2017: Exploit Details and Patch Workaround

The September 2017 Microsoft Internet Explorer information disclosure vulnerability exposed kernel memory to attackers, turning browsing sessions into data theft opportunities.

Imagine a hacker silently siphoning your passwords or documents just by luring you to a malicious site—no download, no warning. This wasn’t theoretical; proof-of-concept exploits circulated within weeks of Microsoft’s patch release, targeting IE 11 on Windows 7 through 10.

At its core, the flaw let attackers bypass ASLR protections and leak memory addresses, making it a prime tool for escalating privileges. Even with Microsoft’s KB4041676 update, many systems remained unpatched due to legacy dependencies.

Here’s how the exploit worked, why it spread so fast, and the three critical steps to lock down your systems—whether you’re still using IE or just cleaning up old vulnerabilities.

How the September 2017 Internet Explorer information disclosure vulnerability works: exploit method and attack vectors

The September 2017 Internet Explorer information disclosure vulnerability (CVE-2017-8759) exploited a memory corruption flaw in Microsoft Edge’s Chakra JavaScript engine—even though it affected Internet Explorer 11. This vulnerability allowed attackers to leak kernel memory addresses, bypassing Address Space Layout Randomization (ASLR) protections.

The flaw stemmed from improper handling of object references during JavaScript garbage collection, enabling precise memory address disclosure.

Attackers could craft malicious websites or drive-by download attacks to trigger the vulnerability. When a victim visited an infected page, IE 11 would execute heap spray techniques to manipulate memory structures, leaking virtual memory addresses back to the attacker.

These addresses helped bypass ASLR, a core Windows security feature designed to prevent memory-based exploits.

Here’s how the exploit chain worked in affected Windows 7/8.1/10 systems running IE 11:

1. Memory Leak Trigger: Malicious JavaScript forced IE to disclose kernel memory addresses via use-after-free bugs in Chakra.
2. ASLR Bypass: Leaked addresses allowed attackers to predict DLL locations in memory.
3. Arbitrary Code Execution: With memory layout known, attackers could craft ROP chains for privilege escalation.

The vulnerability was particularly dangerous because it didn’t require user interaction beyond visiting a malicious page. Attackers could embed exploits in fake update prompts or ad networks, making it a highly scalable threat. Microsoft’s September 2017 Patch Tuesday addressed the flaw via KB4041676, but many enterprises delayed updates, leaving systems exposed for months.

Real-world attack scenarios included:

• Watering Hole Attacks: Compromising legitimate sites frequented by targets (e.g., industry forums).
• Malvertising Campaigns: Injecting exploits into legitimate ads served via IE.
• Phishing Kits: Using leaked memory addresses to bypass sandboxing in Windows Defender Application Control (WDAC).

Microsoft’s patch fixed the issue by isolating Chakra’s memory management and enforcing stricter ASLR policies. However, the vulnerability highlighted a critical flaw: IE 11’s shared engine with Edge meant vulnerabilities in one could affect the other. This led Microsoft to accelerate IE’s deprecation, pushing users toward Microsoft Edge (Chromium-based) as the safer alternative.

To mitigate risks, I recommend disabling IE 11 if unused and enforcing browser policies via Group Policy to block legacy versions. For systems still requiring IE, EMET (Enhanced Mitigation Experience Toolkit) could provide temporary protections by hardening memory access controls until patches were applied.

Understanding this exploit method underscores why modern browsers prioritize sandboxing and memory isolation—lessons IE 11 failed to implement effectively. 🖥️

Step-by-step guide: how to apply the official Microsoft patch and alternative workarounds

Microsoft released the cumulative security update KB4041676 in September 2017 to address the Internet Explorer information disclosure vulnerability (CVE-2017-8759). This patch fixes memory corruption flaws that could leak kernel data to malicious websites.

If you’re running Windows 7/8.1/10 with IE 11, follow these steps to apply the patch or use alternative mitigations if updates aren’t immediately available.

Before proceeding, verify your Windows version and IE 11 installation via Win + R → winver and Internet Options → Advanced. Unsupported systems (e.g., Windows XP) require manual registry tweaks or third-party tools like EMET (Enhanced Mitigation Experience Toolkit) for temporary protection.

For enterprise environments, deploy the patch via WSUS (Windows Server Update Services) or System Center Configuration Manager. Test the patch on a non-production machine first to avoid compatibility issues with legacy applications relying on IE’s outdated rendering engine.

If patching isn’t feasible, switch to Microsoft Edge or Google Chrome immediately. Edge mitigates this vulnerability through modern sandboxing, while Chrome’s V8 engine isn’t affected. For critical systems, combine EMET with firewall rules to block IE from accessing untrusted sites.

Monitor Microsoft’s Security Response Center for updates on CVE-2017-8759. The patch is cumulative, so future updates will include this fix automatically. Always prioritize security updates over optional feature updates to protect against evolving threats.