CVE-2026-68198: Linux Kernel Use-After-Free Vulnerability

CVE-2026-68198 Overview

CVE-2026-68198 is a use-after-free vulnerability in the Linux kernel's ath6kl Wi-Fi driver. The flaw resides in the aggr_reset_state() function, which manages 802.11 aggregation state teardown. The function invokes timer_delete() non-synchronously against the aggregation timer before freeing the associated aggr_conn structure. A concurrently executing aggr_timeout callback can then dereference freed memory in rx_tid[] and stat[] fields. The callback can also re-arm itself through mod_timer() while teardown proceeds, compounding the race.

Critical Impact
An adjacent-network attacker can trigger memory corruption in the kernel, potentially leading to arbitrary code execution or denial of service on affected Linux systems using ath6kl Wi-Fi hardware.

Affected Products

Linux kernel branches containing the ath6kl wireless driver prior to the fix commits
Systems using Atheros AR6003/AR6004-based Wi-Fi hardware managed by ath6kl
Embedded and IoT devices shipping vulnerable Linux kernel versions

Discovery Timeline

2026-08-10 - CVE-2026-68198 published to NVD
2026-08-13 - Last updated in NVD database

Technical Details for CVE-2026-68198

Vulnerability Analysis

The vulnerability is a classic use-after-free race condition in kernel timer teardown logic. The aggr_reset_state() function in the ath6kl driver calls timer_delete() to cancel the aggregation timer. This variant does not wait for an in-flight timer callback to complete before returning. Callers such as aggr_module_destroy() then proceed to kfree(aggr_info->aggr_conn), releasing memory the timer callback may still be actively reading or writing.

When aggr_timeout runs concurrently, it accesses aggr_conn fields including the per-TID receive state array rx_tid[] and the statistics array stat[]. Any dereference after the free constitutes a use-after-free primitive. The callback can further invoke mod_timer() to re-arm itself, which introduces a second race window where a stale timer is queued against freed memory.

Root Cause

The root cause is the use of the non-synchronous timer_delete() API in a teardown path that immediately proceeds to free the object owning the timer. Correct teardown requires timer_delete_sync(), which guarantees any executing callback has finished before returning. This pattern is a known-hazardous idiom flagged repeatedly in Linux kernel review.

Attack Vector

Exploitation requires adjacent-network access, meaning the attacker must be within Wi-Fi range or otherwise able to interact with the wireless interface at layer 2. An attacker can send crafted 802.11 aggregation-related frames or induce state transitions that cause the driver to reset aggregation state while the timer is armed. Winning the race yields kernel memory corruption. No user interaction or privileges are required. The vulnerability mechanism is documented in the kernel git commits referenced below.

See the upstream fix in Kernel Git Commit ba7debb4 for the definitive technical description.

Detection Methods for CVE-2026-68198

Indicators of Compromise

Unexpected kernel oops, panic, or KASAN reports referencing aggr_timeout, aggr_reset_state, or ath6kl symbols
Wireless interface resets or repeated driver reinitialization on ath6kl-backed hardware
Kernel logs showing slab-use-after-free warnings tied to aggr_conn allocations

Detection Strategies

Enable CONFIG_KASAN and CONFIG_DEBUG_OBJECTS_TIMERS on test systems to surface the race deterministically during fuzzing
Correlate wireless driver crash traces with proximity events indicating adjacent-network activity
Inventory hosts running vulnerable kernel versions with ath6kl loaded via lsmod sweeps

Monitoring Recommendations

Ship kernel ring buffer logs (dmesg, /var/log/kern.log) to a central SIEM and alert on ath6kl and BUG: patterns
Track kernel version and loaded module inventory across endpoints to identify unpatched systems
Monitor for repeated wireless disconnects that may indicate exploitation attempts against the aggregation state machine

How to Mitigate CVE-2026-68198

Immediate Actions Required

Apply the upstream Linux kernel patch that replaces timer_delete() with timer_delete_sync() in aggr_reset_state()
Update to a stable kernel release that incorporates the referenced fix commits
On systems where ath6kl hardware is not required, blacklist the module to remove the attack surface

Patch Information

The fix has been merged across multiple stable branches. Reference commits: Kernel Git Commit 18965470, Kernel Git Commit 64af6534, Kernel Git Commit a3313111, Kernel Git Commit b5d618fd, and Kernel Git Commit ba7debb4. Rebuild and reboot into the patched kernel to activate the fix.

Workarounds

Unload the ath6kl module with modprobe -r ath6kl_core ath6kl_sdio ath6kl_usb on systems where wireless is not needed
Add ath6kl_core to /etc/modprobe.d/blacklist.conf to prevent automatic loading at boot
Restrict physical proximity and disable Wi-Fi radios on affected devices until patching completes

bash

# Blacklist the vulnerable driver until the patched kernel is deployed
echo "blacklist ath6kl_core" | sudo tee /etc/modprobe.d/ath6kl-blacklist.conf
echo "blacklist ath6kl_sdio" | sudo tee -a /etc/modprobe.d/ath6kl-blacklist.conf
echo "blacklist ath6kl_usb"  | sudo tee -a /etc/modprobe.d/ath6kl-blacklist.conf
sudo modprobe -r ath6kl_usb ath6kl_sdio ath6kl_core 2>/dev/null
sudo update-initramfs -u