CVE-2026-68373: wifi: at76c50x-usb: avoid length underflow in at76_guess_freq()

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2026-68373 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.30 with commit 1264b951463a00efebe1bb596499aaad620ec8af and fixed in 6.6.148 with commit e165a1d295e7e814e13b0f92c86e5d48309509ce
	Issue introduced in 2.6.30 with commit 1264b951463a00efebe1bb596499aaad620ec8af and fixed in 6.12.101 with commit bcde7249d45f52f994a9872bedf45994472ade77
	Issue introduced in 2.6.30 with commit 1264b951463a00efebe1bb596499aaad620ec8af and fixed in 6.18.42 with commit fb1b50ab699211e777dca5ccfb648788b6a6e519
	Issue introduced in 2.6.30 with commit 1264b951463a00efebe1bb596499aaad620ec8af and fixed in 7.1.6 with commit f742d9c98b5c504fc9e6744eef13a721c2aea486
	Issue introduced in 2.6.30 with commit 1264b951463a00efebe1bb596499aaad620ec8af and fixed in 7.2-rc5 with commit 61a799ffd1e5a4fd3702d547828b7ff3d161468e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68373
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/net/wireless/atmel/at76c50x-usb.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/e165a1d295e7e814e13b0f92c86e5d48309509ce
	https://git.kernel.org/stable/c/bcde7249d45f52f994a9872bedf45994472ade77
	https://git.kernel.org/stable/c/fb1b50ab699211e777dca5ccfb648788b6a6e519
	https://git.kernel.org/stable/c/f742d9c98b5c504fc9e6744eef13a721c2aea486
	https://git.kernel.org/stable/c/61a799ffd1e5a4fd3702d547828b7ff3d161468e