Medium [CVE-2026-68373] Linux kernel: Out-of-bounds read in wifi driver due to length underflow

In the Linux kernel, the following vulnerability has been resolved: wifi: at76c50x-usb: avoid length underflow in at76_guess_freq() at76_guess_freq() checks only that the received frame is at least a bare 802.11 header (24 bytes) before subtracting the fixed management-body offset: len -= el_off; For both beacon and probe response frames, el_off is 36.

If the frame is shorter than el_off, subtracting it causes the calculated IE length to wrap. The length is eventually passed to cfg80211_find_elem_match() as a very large unsigned value, so the element walk runs beyond the RX skb.

This path is reached from at76_rx_tasklet() while scanning. If the device delivers a truncated beacon or probe response, the oversized IE length causes an out-of-bounds read during scanning.

Skip the IE lookup if the frame does not reach the variable elements, before subtracting el_off. A remote attacker could exploit a length underflow vulnerability in the `at76_guess_freq()` function by sending a specially crafted Wi-Fi frame.

This can cause an out-of-bounds read during the scanning process, potentially leading to a denial of service or the disclosure of sensitive information. Red Hat severity: Important — CVSS 5.9 (CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H).

Weakness: CWE-125.