In early 2022, a dangerous vulnerability was uncovered in the Wi-Fi firmware stack for certain popular devices. Identified as CVE-2022-21745 (Patch ID: ALPS06468872, Issue ID: ALPS06468872), this bug allows an attacker to remotely escalate their privileges simply by running a malicious Wi-Fi hotspot. No other permissions are required, and the device user doesn’t have to do anything except connect.

This long-form analysis will cover the vulnerability’s root cause, provide example code, link to references, and show how it can be practically exploited. We’ll keep the technical talk simple and focus on how you can understand -- and protect yourself from -- this real-world threat.

Where Does It Happen?

The bug occurs in the firmware that handles Wi-Fi connections on affected chipsets (most notably in MediaTek platforms as indicated by the patch reference). When your device tries to connect to a crafted Wi-Fi hotspot, the attacker can send packets that trigger this use-after-free.

What’s a “Use After Free”?

Wi-Fi firmware often keeps track of connections and various objects in memory. Sometimes when a connection is ended or reset, the memory is “freed” (returned back for use). If the firmware later tries to use a pointer to the freed memory (“use after free”), it might accidentally corrupt memory or let an attacker run code.

Below is a simplified representation of what could go wrong in the firmware

struct wifi_conn *conn = allocate_connection();
// ...
free(conn);
// ...
// Oops: use after free
if (conn->state == CONNECTED) {    // conn points to freed memory!
    escalate_privileges();
}

A real-world exploit would abuse the window between when the connection pointer is freed and when it’s later reused, sometimes by quickly recycling Wi-Fi connections or by flooding specially crafted packets.

Let’s walk through a simple version of the exploit

1. Attacker sets up a malicious Wi-Fi hotspot using a laptop with custom software like hostapd.

Device user scans and connects to the hotspot as if it were any public Wi-Fi.

3. The attacker’s hotspot sends packets that exploit the use-after-free bug, tricking the firmware into reusing freed memory.
4. Attacker’s data is injected where privileged code is executed in the context of the Wi-Fi firmware.
5. Device is now compromised with attacker’s code running, possibly breaking sandboxing and gaining higher-level access.

Proof-of-Concept Snippet (Python for Beacon Flood)

*This snippet does not exploit the bug directly but demonstrates flooding a Wi-Fi device with custom crafted beacons, a step attackers might use to trigger memory handling bugs:*

from scapy.all import *

iface = "wlanmon"
ssid  = "malicious_ap"

dot11 = Dot11(type=, subtype=8, addr1='ff:ff:ff:ff:ff:ff',
                addr2=RandMAC(), addr3=RandMAC())

beacon = Dot11Beacon()
essid  = Dot11Elt(ID="SSID", info=ssid, len=len(ssid))
frame  = RadioTap()/dot11/beacon/essid

while True:
    sendp(frame, iface=iface, inter=.1, loop=1)

Attackers would go further by customizing information elements and frame sequences to specifically hit the vulnerable code path shown above.

Original References

- MediaTek Security Bulletins – ALPS06468872
- CVE Database Entry for CVE-2022-21745
- hostapd – User space daemon for wireless access points
- Understanding Use-After-Free Vulnerabilities

How To Protect Yourself

- Apply patches: Always update your device firmware. The fix for this bug is included in the patch ID mentioned above.

Avoid unknown Wi-Fi hotspots: Only connect to networks you trust.

- Disable auto-connect: Prevent your device from auto-connecting to open or suspicious public Wi-Fi.
- Monitor manufacturer/security advisories for your device.

Conclusion

CVE-2022-21745 is an example of why firmware security is crucial. A single memory bug in the Wi-Fi stack can let a nearby attacker take control of your device, no clicks or permissions required. If you haven’t already applied the manufacturer’s patch, you should do so immediately.  

For researchers, this case underscores how everyday over-the-air protocols like Wi-Fi can carry severe hidden risks, and vigilance is needed on both defense and attack research.

Timeline

Published on: 06/06/2022 18:15:00 UTC
Last modified on: 06/13/2022 18:47:00 UTC