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CVE-2026-68373
wifi: at76c50x-usb: avoid length underflow in at76_guess_freq()
Published 2026-08-10 (2 months 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-2026-68373 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
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/atmel/at76c50x-usb.c
- What this is
- NETWORKING DRIVERS (WIRELESS)MAINTAINERS section matched on drivers/net/wireless/ · linux-wireless@vger.kernel.org · Maintained
- Kernel module
- at76c50x_usb
Check it on the machine
grep -wE 'CONFIG_AT76C50X_USB|CONFIG_WLAN|CONFIG_WLAN_VENDOR_ATMEL' /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 at76c50x_usbPrints 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
- trixie, 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_AT76C50X_USB, CONFIG_WLAN, CONFIG_WLAN_VENDOR_ATMEL
- 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
- 2026-08-10 (2 months ago)source
- CVSS
- 8.1 high
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- adjacent network (AV:A)source
- EPSS
- 0.27%, higher than 18.5% 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 |
|---|---|---|
| 2.6.30 | 5.10.265 | cb831aff2f85 |
| 2.6.30 | 5.15.216 | 4875680d1703 |
| 2.6.30 | 6.1.183 | b406f33d234f |
| 2.6.30 | 6.6.148 | e165a1d295e7 |
| 2.6.30 | 6.12.101 | bcde7249d45f |
| 2.6.30 | 6.18.42 | fb1b50ab6992 |
| 2.6.30 | 7.1.6 | f742d9c98b5c |
| 2.6.30 | 7.2 | 61a799ffd1e5 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | 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
- The malformed frame is an over-the-air 802.11 beacon or probe response received by the at76c50x USB WLAN dongle and parsed in at76_rx_tasklet(); an attacker only needs to be within radio range of the victim, which is the adjacent-network (WiFi frame injection) case.
- AC:LAttack complexity, low
- The attacker simply transmits a beacon/probe response whose body is shorter than the 36-byte fixed management offset with a valid FCS, and can repeat it continuously or answer the victim's probe requests during the routine scans that set priv->scanning, so triggering is reliable and fully attacker-timed.
- PR:NPrivileges required, none
- No authentication, association, or any local privilege is required; the frame is parsed during scanning before any association or key exchange, so an entirely unauthenticated radio-range attacker reaches the bug.
- UI:NUser interaction, none
- Background and periodic scans are issued automatically by wpa_supplicant/NetworkManager without any user action, so no victim interaction is needed for the vulnerable path to run.
- S:UScope, unchanged
- The out-of-bounds read stays within the kernel's own memory and security authority; no VM, IOMMU, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- The underflowed length becomes ~4GB when widened to unsigned int, so the element walk reads far past the ~2.5KB RX skb slab object, and the out-of-bounds byte taken as el[2] is turned into rx_status.freq that userspace observes in scan results, allowing repeated frames to leak adjacent kernel heap contents.
- I:NIntegrity impact, none
- The defect is purely a read overrun; nothing outside the skb is written and the only attacker-influenced value is the reported channel/frequency, giving no memory-corruption or control-flow primitive.
- A:HAvailability impact, high
- The unbounded element walk runs off the slab and can dereference unmapped memory while executing in tasklet/softirq context, producing a kernel oops or panic that the attacker can trigger repeatedly with injected frames.