Affected: Linux

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.