CVE-2023-21287 - Remote Code Execution via Type Confusion – Details, Exploit, and Don’t Get Burned

---

Security flaws with the potential for remote code execution (RCE) can be among the nastiest you’ll bump into, and 2023 had its share of bad ones. CVE-2023-21287 is a critical-severity vulnerability in Android’s system that allows malicious parties to execute code on a victim device—no permissions needed, no trick clicks required. If you’re running affected Android versions, or you develop software for Android, this is a must-read.

What Is CVE-2023-21287?

CVE-2023-21287 is a vulnerability affecting Android's system, specifically in the Android Framework. The root cause is a classic *type confusion* bug present in several code locations. By exploiting this weakness, an attacker can hijack program flow and execute arbitrary code with system privileges.

Why Is This Serious?

- Remote code execution: Attackers can run their own code on your device, potentially stealing data or installing malware.

Technical Details: Understanding Type Confusion

Type confusion vulnerabilities happen when the program assumes a variable is one type, but it’s actually another. This leads to unpredictable behavior, often allowing attackers to hijack program control.

In this case, the Android Framework mishandled certain objects in its libraries. Let’s look at a simplified code example:

// Vulnerable: Imagine this is a simplified part of the Framework

public void handleParcel(Parcel parcel) {
    Object obj = parcel.readValue(getClass().getClassLoader());
    // The following line assumes 'obj' is of type Foo
    Foo foo = (Foo) obj;
    foo.doFooThings(); // If 'obj' isn't really a Foo, anything could happen!
}

If an attacker crafts a special Parcel that tricks the system into reading an object of type Bar (instead of Foo), then type confusion occurs. The program tries to execute code on Bar objects as if they were Foo—potentially leading to arbitrary code execution.

Official Android code references and the locations impacted:
- Android Security Bulletin—October 2023
- Security Patch Detail at AOSP

Prerequisites

- Attackers need some way to send a crafted Parcel to a targeted Android component. Usually, this means access to an exposed IPC service or a system intent.

Proof of Concept Insight

While Google hasn't published a step-by-step PoC (proof of concept), security researchers have walked through rough exploit routes. Here’s a basic outline:

1. Craft a special input to the exposed IPC interface, containing a malicious object masquerading as an expected type.
2. Trigger code that deserializes/interprets the object without strict type checking.
3. Hijack program flow — Once the program starts operating on the wrong type, the attacker can use techniques (such as writing a malicious class with unexpected fields or methods) to influence memory and gain code execution.

Minimal Exploit Snippet (Psuedocode)

# This is a Python pseudocode for proof of concept, for demonstration only

import socket

def send_malicious_parcel(target_ip, port):
    parcel = craft_parcel_with_bad_object()  # Create object with malicious code
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((target_ip, port))
    s.send(parcel)
    s.close()

# The craft_parcel_with_bad_object() would need to exploit the Android framework's native parcel format

*Note: Actual exploitation requires deep knowledge of Android’s IPC and Parcel mechanisms. This is a simplified view to illustrate the attack approach.*

How To Protect Yourself

- Update now! Android has patched this vulnerability starting with the October 2023 Security Patch. If your device maker or ROM supplier supports it, install this update ASAP.
- Limit app permissions: Don’t install weird apps from untrusted sources, even though this bug is privileged enough to work without them.
- Stay off insecure WiFi: Until updated, stay cautious about public or open networks, as these bugs are sometimes used for network-based attacks.

References & Original Sources

- CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-21287
- Android Security Bulletin: https://source.android.com/docs/security/bulletin/2023-10-01
- Patch Code: https://android.googlesource.com/platform/frameworks/base/+/b0666a6e4f9fb5cd8e39036e67e6debba721eefd
- Type Confusion Explanations: OWASP

Conclusion

CVE-2023-21287 is a dangerous example of how subtle bugs can expose millions of Android users to remote exploitation. Type confusion is hard to spot and even harder to mitigate without strong coding standards. Keep your devices up to date, and if you’re a developer, review any code that handles object deserialization or IPC for similar issues.

Timeline

Published on: 08/14/2023 22:15:00 UTC
Last modified on: 08/21/2023 18:17:00 UTC