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CVE-2026-74678
net: usb: ax88179_178a: fix skb leak in ax88179_tx_fixup()
Published 2026-08-22 (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-2026-74678 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 | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
When the interface has NETIF_F_SG enabled and skb_linearize() fails in ax88179_tx_fixup(), the function returns NULL without freeing the skb. usbnet_start_xmit() treats a NULL return from tx_fixup() as a drop (info->flags does not set FLAG_MULTI_PACKET for this driver), jumping to the "drop" label where it does `if (skb) dev_kfree_skb_any(skb)`. Because tx_fixup() returned NULL, the local skb variable in usbnet_start_xmit() is NULL, so the original skb is never freed — a memory leak on every TX frame whose linearization fails (i.e. under memory pressure). Free the skb before returning, matching the error handling already used for the pskb_expand_head() failure path in the same function.
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/usb/ax88179_178a.c
- What this is
- USB NETWORKING DRIVERSMAINTAINERS section matched on drivers/net/usb/ · linux-usb@vger.kernel.org · Odd Fixes
- Kernel module
- ax88179_178a
Check it on the machine
grep -wE 'CONFIG_USB_NET_AX88179_178A|CONFIG_USB_NET_DRIVERS' /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 ax88179_178aPrints 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.
- bookworm, trixie, forky, sid, 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_USB_NET_AX88179_178A, CONFIG_USB_NET_DRIVERS
- 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
- 2026-08-22 (2 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.48%, higher than 39.9% 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 |
|---|---|---|
| 5.17 | 6.1.183 | 83a765cbd7b4 |
| 5.17 | 6.6.152 | 1c63303659a2 |
| 5.17 | 6.12.104 | 2be5091fa693 |
| 5.17 | 6.18.45 | 58733b1dd46b |
| 5.17 | 7.1.9 | 4039cd807a5a |
| 5.17 | 7.2 | 1f428e309473 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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:NAttack vector, network
- On systems using the common ASIX AX88179/AX88178A USB 3.0 GbE adapter as their uplink, remote peers induce outbound TSO/GSO traffic that reaches ax88179_tx_fixup() via __dev_queue_xmit→netdev_start_xmit→usbnet_start_xmit; attacker-supplied or reply traffic over the bound NIC is standard network reachability.
- AC:LAttack complexity, low
- NETIF_F_SG and NETIF_F_TSO are always enabled at bind; an attacker can send non-linear egress skbs and deliberately exhaust GFP_ATOMIC/slab memory so skb_linearize() fails on demand—both prerequisites are fully under attacker control without races or rare layout.
- PR:NPrivileges required, none
- No capability or authentication gates the netdev TX path; any remote host exchanging IP traffic with a victim whose ax88179 interface is up can trigger usbnet_start_xmit without local shell access, credentials, or init-namespace privileges.
- UI:NUser interaction, none
- Exploitation needs only that the adapter is plugged in and carrying traffic—the normal always-on state for USB-Ethernet docks, kiosks, and laptops—not any one-time victim action such as mounting media or opening a file.
- S:UScope, unchanged
- Leaked sk_buff objects remain in kernel SLAB caches within the same kernel security authority; there is no VM escape, container breakout, IOMMU bypass, or cross-boundary corruption.
- C:NConfidentiality impact, none
- Orphaned skbs are not freed but are not exposed to userspace or adjacent objects; there is no out-of-bounds read, use-after-free, or other disclosure primitive—only silent kernel heap consumption.
- I:NIntegrity impact, none
- The defect drops an skb reference on an error return without corrupting heap metadata, overwriting kernel objects, or enabling arbitrary writes or control-flow hijacking.
- A:HAvailability impact, high
- Each skb_linearize() failure permanently leaks one skb; under attacker-driven memory pressure an unauthenticated remote peer can repeat TSO egress to exhaust kernel memory, provoking OOM-killer thrashing and denial of service on the host.