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CVE-2026-74325
wifi: mt76: use kfree_rcu for offchannel link in mt76_put_vif_phy_link
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74325 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
mt76_put_vif_phy_link() frees the offchannel mlink with plain kfree() after rcu_assign_pointer(NULL). However, rcu_assign_pointer only prevents future RCU readers from obtaining the pointer -- it does not wait for existing readers that already hold it via rcu_dereference. The TX datapath (e.g. mt7996_mac_write_txwi) dereferences mlink->wcid and mlink->idx under rcu_read_lock. If a TX softirq obtained the pointer via rcu_dereference just before the NULL assignment, it will dereference freed memory after the kfree. struct mt76_vif_link already contains an rcu_head field that is unused at this free site -- a developer oversight, since the adjacent kfree_rcu_mightsleep call for rx_sc in the same function shows the pattern was understood. Replace kfree(mlink) with kfree_rcu(mlink, rcu_head).
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/net/wireless/mediatek/mt76/channel.c
- What this is
- MEDIATEK MT76 WIRELESS LAN DRIVERMAINTAINERS section matched on drivers/net/wireless/mediatek/mt76/ · linux-wireless@vger.kernel.org · Maintained
- Kernel module
- mt76
Check it on the machine
grep -wE 'CONFIG_MT76_CORE|CONFIG_WLAN|CONFIG_WLAN_VENDOR_MEDIATEK' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w mt76Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x
- ?
- not established - no Makefile entry for the affected file
- M
- a module where it is built at all; some flavours do not build it
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_MT76_CORE, CONFIG_WLAN, CONFIG_WLAN_VENDOR_MEDIATEK
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.14 | 6.18.40 | c7a83899203e |
| 6.14 | 7.1.5 | 50e700ac0edc |
| 6.14 | 7.2 | 7fae097aa9a5 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is reached only through local nl80211/genl paths (NL80211_CMD_REMAIN_ON_CHANNEL, CANCEL_REMAIN_ON_CHANNEL, TRIGGER_SCAN) that call mt76_put_vif_phy_link during ROC/scan teardown; remote WiFi frames cannot invoke this free path.
- AC:LAttack complexity, low
- Exploitation is a race between ROC/scan completion freeing the offchannel mlink and the TX datapath still dereferencing it under RCU; an attacker with nl80211 access controls both sides by starting offchannel ops, queuing offchannel TX, and cancelling ROC concurrently.
- PR:LPrivileges required, low
- Entry points require GENL_UNS_ADMIN_PERM (CAP_NET_ADMIN in the socket user namespace). Per CNA guidance this is Low because unprivileged users can obtain CAP_NET_ADMIN via user namespaces and drive ROC/scan on an mt76 multi-radio interface they control.
- UI:NUser interaction, none
- No victim interaction is required once the attacker can issue nl80211 ROC/scan commands and offchannel TX; exploitation does not depend on a user opening files, mounting filesystems, or clicking prompts.
- S:UScope, unchanged
- Impact is confined to kernel memory corruption and privilege escalation within the same OS security boundary; it does not cross VM, container, or IOMMU isolation boundaries on its own.
- C:HConfidentiality impact, high
- This is a use-after-free of struct mt76_vif_link freed via kfree while TX paths such as mt7996_mac_write_txwi still rcu_dereference and read mlink fields; UAF enables heap grooming for arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- Freed mlink contents control TXWI fields (omac_idx, wmm_idx, band_idx, bss idx) passed to firmware DMA descriptors; UAF provides a practical path to corrupt kernel heap metadata and achieve arbitrary code execution.
- A:HAvailability impact, high
- Dereferencing the freed offchannel_link in the TX worker/softirq path causes kernel oops or panic; UAF on a hot transmit path can crash multi-radio mt76 APs, routers, and client devices during P2P/scan offchannel operations.