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CVE-2026-90372
wifi: mt76: mt7915: avoid nss underflow in mt7915_mcu_get_sta_nss
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-90372 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 | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
If a peer's VHT/HE MCS map has no supported spatial stream (all fields 0x3), the loop exits with nss == 0 and the function returned (u8)-1 (255), which was then written into the firmware sta_rec_bf beamforming fields. Clamp the result to 0.
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/mt7915/mcu.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
- mt7915e
Check it on the machine
grep -wE 'CONFIG_MT76_CORE|CONFIG_MT7915E|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 mt7915ePrints 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.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixieMnot built on amd64/cloud-amd64, arm64/cloud-arm64, armel/rpi, s390x/s390x
- forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x
- bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_MT76_CORE, CONFIG_MT7915E, 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
- 2026-09-17 (31 days ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:Hsource recompute it - Attack vector
- adjacent network (AV:A)source
- EPSS
- 0.36%, higher than 27.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 5.8 | 5.10.270 | 2801477c36a1 |
| 5.8 | 5.15.221 | 38f4d6323bcd |
| 5.8 | 6.1.188 | 25f753f7f620 |
| 5.8 | 6.6.157 | e63c6291ecdd |
| 5.8 | 6.12.110 | 85bd46ab7674 |
| 5.8 | 6.18.52 | 6ce78d04c7ea |
| 5.8 | 7.2.6 | ecfd1a07e78c |
| 5.8 | 7.3 | 4a2f4be532e3 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
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:AAttack vector, adjacent network
- A nearby 802.11 peer supplies the malformed MCS map in the HE Capabilities MCS NSS field of an Association Request. hostapd's NL80211_CMD_NEW_STATION reaches ieee80211_add_station()→sta_link_apply_parameters(), which copies he_mcs_nss_supp; mt76_sta_state(AUTH→ASSOC) then calls mt7915_mcu_get_sta_nss() on that map. WiFi radio range is Adjacent.
- AC:LAttack complexity, low
- The attacker sets every 2-bit NSS field in HE rx_mcs_80 or rx_mcs_160 to 0x3. mt7915_mcu_get_sta_nss() then leaves its nss=8..1 loop with nss==0 and returns (u8)-1 (255) on every association. mac80211 does not reject an all-0x3 HE MCS map (unlike the 0xFFFF VHT check in ieee80211_vht_cap_ie_to_sta_vht_cap()). No race is involved.
- PR:NPrivileges required, none
- mt7915_mac_sta_event(MT76_STA_EVENT_ASSOC) runs from sta_info_move_state(IEEE80211_STA_ASSOC) when hostapd's NL80211_CMD_NEW_STATION sets ASSOCIATED, before AUTHORIZED (the WPA 4-way handshake). 802.11 Open System authentication does not require a PSK or SAE credential on this path.
- UI:NUser interaction, none
- The attacker transmits the Association Request. ieee80211_add_station() and mt7915_mcu_add_sta() run in the AP kernel with no operator action on the victim device.
- S:UScope, unchanged
- The underflowed NSS is stored in the kernel sta_rec_bf TLV and sent to the on-device mt7915 MCU via MCU_EXT_CMD(STA_REC_UPDATE). Impact stays in the same kernel/device authority; this is not a VM, IOMMU, or sandbox escape.
- C:NConfidentiality impact, none
- mt7915_mcu_get_sta_nss() only derives a u8 from the peer MCS map. That 255 is stored in sta_rec_bf.ncol_gt_bw80 or ibf_ncol; ncol used to index matrix[4][4] is min()'d with nrow, so there is no kernel OOB read and nothing is returned over the air.
- I:LIntegrity impact, low
- mt7915_mcu_sta_bfer_he() writes the underflowed nss_mcs (255) directly to sta_rec_bf.ncol_gt_bw80 on 160 MHz, and the implicit-VHT path writes it to ibf_ncol, then mt7915_mcu_add_sta() sends that TLV to firmware. That is a limited corruption of the chip beamforming profile, not an arbitrary kernel write.
- A:HAvailability impact, high
- ncol_gt_bw80 and ibf_ncol are NSS counts the mt7915 MCU uses as beamforming dimensions. 255 is far outside the 0–3 range implied by the driver's matrix[4][4], so the firmware can hang or crash and take the radio down, and the peer can retrigger it on every association.