CVE-2026-68402: wifi: cfg80211: bound element ID read when checking non-inheritance

In the Linux kernel, the following vulnerability has been resolved:

wifi: cfg80211: bound element ID read when checking non-inheritance

cfg80211iselementinherited() reads the first data octet of the candidate element (id = elem->data[0]) to look it up in an extension non-inheritance list. It does so after testing elem->id, but without verifying that the element actually has a data octet. A zero-length extension element (WLANEIDEXTENSION with length 0) therefore makes it read one octet past the end of the element.

ieee80211parseelemsfull() runs this check for every element of a frame once a non-inheritance context exists -- e.g. while parsing a per-STA profile of a Multi-Link element in a (re)association response, or a non-transmitted BSS profile -- so a crafted frame from an AP can trigger a one-octet slab-out-of-bounds read during element parsing:

BUG: KASAN: slab-out-of-bounds in cfg80211iselementinherited Read of size 1 ... in net/wireless/scan.c

Return early (treat the element as inherited) when an extension element carries no data, mirroring the existing handling of empty ID lists.

The bug was found by fuzzing ieee80211parseelemsfull() under KASAN.