CVE-2022-41568 - Crashing LINE for iOS via Invalid E2EE Shared Key

The messaging app LINE is one of the most popular chat platforms, especially in East Asia. Like other major messengers, it offers "end-to-end encryption" (E2EE) to keep group chats private. However, a flaw tracked as CVE-2022-41568 exposed users to a simple-yet-serious crash bug – all an attacker needed to do was share a malformed encryption key in a group chat, potentially crashing the LINE app for anyone running iOS versions before 12.17.. In this article, we break down what went wrong, how the bug works, and how attackers might have exploited it, along with practical code and references.

What is CVE-2022-41568?

- CVE ID: CVE-2022-41568

The E2EE Key Exchange – Quick Primer

LINE uses a protocol called E2EE (Letter Sealing) to encrypt all messages within a group chat. For group messaging, LINE clients exchange a shared secret (aka "shared key") so everyone can decrypt messages.

What went wrong?
If a member shared a "bad" (invalid) shared key, the LINE app on iOS would not check the key's structure robustly. As a result, it could fail catastrophically when trying to process it, leading to a crash.

The iOS LINE app accepted shared keys for group E2EE.

- No strong validation: The app would not always check if these keys were valid or correctly formatted.
- When an invalid shared key entered the group context, the client would try to process it – and likely throw an exception or hit a low-level error, like buffer overflows or bad memory access, causing a crash.

For attackers, all you had to do was send a crafted message encoding a bogus shared key to the group chat. Everyone's iOS LINE (older than 12.17.) would try to process it, and their app would crash instantly.

Code Example: Simulating the Attack

> (Warning: Never attack others' privacy or devices. This is for educational purposes only.)

While the full protocol is closed-source, researchers simulated the bug by sending malformed key packets using a modified client or proxy, as shown below:

import socket

# Pre-craft a fake shared key message
malformed_key_data = b'\x00\xFF\xAA\xBB'  # Invalid / random bytes

def send_malformed_key(group_chat_address, port):
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect((group_chat_address, port))
        # Construct message in the format expected by LINE's protocol, but with the invalid key
        message = b"SHARED_KEY_EXCHANGE:" + malformed_key_data
        s.sendall(message)
        print("Sent malformed shared key to group chat.")

# Fake group chat host & port (for demonstration)
send_malformed_key('127...1', 500)

In real situations, this could be done by altering intercepting traffic with mitmproxy or a custom client.

Proof-of-Concept Text Packet

You could also draft messages simulating key exchange packets. A minimal, illustrative example (not real packet):

{
    "type": "E2EEE_KEY",
    "keydata": "!!BADKEYJUNK!!"
}

When such a message is inserted in the protocol stream, the iOS client expects proper structure but encounters unexpected chunk, triggering a crash.

References & Further Reading

- NVD Entry – CVE-2022-41568
- LINE's Security Update
- Related research on Letter Sealing (LINE's E2EE protocol)
- CVE-2022-41568 at MITRE

Mitigation

Update immediately – LINE fixed this in version 12.17.. Just update your LINE app to get rid of this crash risk.

Conclusion

CVE-2022-41568 is a classic example of how weak input validation in chat apps can cause widespread, remote crashes with simple crafted data. Even if your secrets are safe, your messaging app is still only as stable as its protocol parsing. That’s why software updates—and transparency about bugs—are so important.

Stay safe—keep your apps updated!

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Timeline

Published on: 11/29/2022 05:15:00 UTC
Last modified on: 12/02/2022 15:38:00 UTC