In the world of Android vulnerabilities, CVE-2023-20663 is one that could allow an attacker to gain powerful privileges on a device—without any help from the user. This post will explain in simple terms where the bug sits, how it works, where the code goes wrong, and what steps were taken to fix it. We’ll also show a basic exploit scenario, and provide key links for further reading.
What is CVE-2023-20663?
CVE-2023-20663 is an integer overflow bug found in a wireless LAN (WLAN) driver on certain Android devices (notably from MediaTek platforms). The flaw could let a local attacker (someone with access to a compromised app or another local entry point) write beyond the boundary of assigned memory (an out-of-bounds write), resulting in escalation of privilege to system level—that’s one step below full device compromise.
Device interaction: *No user action is needed* for this vulnerability to be exploited.
Issue ID: ALPS07560741
- Reference: NVD Entry for CVE-2023-20663
Why Should You Care?
Privilege escalation bugs like CVE-2023-20663 are serious. They let an attacker running in a limited environment (say, a compromised or malicious app) break out and gain higher-level powers, potentially reading data, installing malware, or controlling the device in subtle ways.
Where is the Bug?
The bug lives inside low-level C code that handles buffers provided by userspace—often, this comes from IOCTL (input/output control) interfaces in the MediaTek WLAN driver code. When a user process requests the allocation or manipulation of a buffer, the code fails to properly validate sizes—leading to an overflow.
Code Example (Simplified)
Below is a *simulated* snippet typifying a code path where the bug could appear. (This is not the actual code, but shows the pattern.)
// (Fake code for explanation)
// User supplies 'user_len', app requests buffer allocation
int wifi_ioctl_handler(struct ioctl_req *req) {
size_t len = req->user_len; // User-controlled length
char *buf;
// Vulnerable check! No validation of 'len'.
buf = kmalloc(len * sizeof(struct data_pkt), GFP_KERNEL);
if (!buf) return -ENOMEM;
// Later: copy_from_user copies 'len' bytes...
copy_from_user(buf, req->user_buf, len);
// ...other processing...
return ;
}
If user_len is very large, the calculation for the allocation can *overflow*, causing a small buffer to be allocated, but copy_from_user will still try to write a huge region—thus corrupting memory.
Result: The attacker can control what memory gets written—and with careful manipulation, could overwrite critical kernel structures, leading to privilege escalation.
Local Code Execution: App talks to the vulnerable driver interface.
3. Trigger Integer Overflow: App supplies a specially crafted value for buffer length in an IOCTL call, e.g., a very large value that causes integer overflow.
4. Out-of-Bounds Write: Driver allocates too-small memory, then writes too much, corrupting nearby kernel memory.
5. Escalation: Attacker overwrites a kernel structure (such as a function pointer), then triggers code execution to gain system privileges.
Here's a minimal kernel-style pseudocode of the failing pattern
// Assume 32-bit platform
#define MAX_PACKET_SIZE xFFFFFFF
#define DANGER_VALUE x10000010 // Large value to cause overflow
size_t length = DANGER_VALUE;
size_t alloc_size = length * sizeof(struct data_pkt);
// If sizeof(struct data_pkt) is 8:
// alloc_size = x10000010 * 8 = x80000080, but overflows to something small!
buf = kmalloc(alloc_size, GFP_KERNEL); // Small, unexpected buffer!
// Next, copy a huge block, overrunning the buffer:
copy_from_user(buf, user_buffer, length * sizeof(struct data_pkt));
// Boom: oob write!
How Was It Fixed?
The patch (see Patch ID ALPS07560741) puts in strong checks on the size of the buffer. It ensures that any math involving size calculation won’t overflow:
Ends the call with an error if suspicious values are found.
Reference:
- MediaTek Security Bulletin (Search for: ALPS07560741)
- Google Android Security Bulletin April 2023
Summary Table
| Field | Value |
|----------------------|------------------------------|
| CVE | CVE-2023-20663 |
| Component | MediaTek WLAN driver |
| Type | Integer overflow, OOB write |
| Privilege required | System (kernel) |
| User interaction | None |
| Patch | ALPS07560741 |
| Exploit availability | Not public, but straightforward |
| Risk | Local escalation, system control |
Conclusion
CVE-2023-20663 shows that even a simple mathematical mistake in kernel code can open the door to powerful attacks. While most users won’t be directly targeted, those with unpatched or older devices remain at risk until Android security updates (April 2023 or later) are installed.
Check integer math for overflows.
If you’re a user:
Make sure your phone gets regular security updates!
Further Reading & References
- NVD Entry: CVE-2023-20663
- MediaTek Security Bulletins
- Android Security Bulletin April 2023
Stay Secure!
Got questions on Android bugs or kernel security? Drop your thoughts below. And keep your devices updated!
Timeline
Published on: 04/06/2023 18:15:00 UTC
Last modified on: 04/13/2023 17:27:00 UTC