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CVE-2026-68338
net/packet: avoid fanout hook re-registration after unregister
Published 2026-08-10 (2 months ago) by the Linux kernel CNA. Subsystem net/packet. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-68338 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
packet_set_ring() temporarily detaches a socket from packet delivery while reconfiguring its ring. It records the previous running state, clears po->num, unregisters the protocol hook when needed, drops po->bind_lock, and later restores po->num and re-registers the hook from the saved was_running value. That unlocked window can race with NETDEV_UNREGISTER. The notifier can observe the socket as not running, skip __unregister_prot_hook(), and invalidate the per-socket binding by setting po->ifindex to -1 and clearing po->prot_hook.dev. A one-member fanout group can still retain its shared fanout hook device pointer. When packet_set_ring() resumes, re-registering solely from the stale was_running state can re-add the fanout hook after the device has been unregistered. Treat po->ifindex == -1 as an invalidated binding after reacquiring po->bind_lock. This is distinct from ifindex 0, the normal unbound/wildcard state: ifindex -1 marks an existing device binding that was invalidated when the device was unregistered. Restore po->num as before, but do not re-register the hook if device unregister already detached the socket.
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.
net/packet/af_packet.c
- What this is
- PACKET SOCKETSMAINTAINERS section matched on net/packet/af_packet.c · Maintained
Check it on the machine
grep -w CONFIG_PACKET /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.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_PACKET
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
- 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
- 0.18%, higher than 6.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/packet
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 3.1 | 5.10.265 | acb40ebfa5c4 |
| 3.1 | 5.15.216 | c820f4b7f2fa |
| 3.1 | 6.1.183 | 4628efbdc7af |
| 3.1 | 6.6.148 | 80ec024d53a0 |
| 3.1 | 6.12.101 | 0a052e0808e0 |
| 3.1 | 6.18.42 | 1bc55c29cd85 |
| 3.1 | 7.1.6 | a885387dae79 |
| 3.1 | 7.2 | 50aff80475ab |
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:LAttack vector, local
- The bug is triggered through local syscalls — creating an AF_PACKET socket, PACKET_FANOUT/bind setsockopt, PACKET_RX_RING setsockopt, and a netlink device unregister — with no remote packet processing involved.
- AC:LAttack complexity, low
- The attacker controls both sides of the race: it issues the packet_set_ring() reconfiguration and deletes the bound netdev in its own netns, and the unlocked window spans synchronize_net() plus the ring swap, making it wide and reliably winnable.
- PR:LPrivileges required, low
- AF_PACKET requires CAP_NET_RAW and device unregistration CAP_NET_ADMIN, but an unprivileged user obtains both via user+network namespaces (unshare -Urn) and can create and delete veth/dummy devices there.
- UI:NUser interaction, none
- The attacker performs every step itself — socket setup, ring reconfiguration and device teardown — with no action required from any other user.
- S:UScope, unchanged
- The stale hook registration and resulting corruption stay within the kernel's own security authority; no hypervisor, IOMMU or other trust boundary is crossed.
- C:HConfidentiality impact, high
- The fanout packet_type is left linked into a net_device that is being torn down, a dangling registration on soon-to-be-freed memory; such stale-pointer state in the ptype lists can be leveraged for kernel memory disclosure.
- I:HIntegrity impact, high
- The dangling list node in the freed net_device's ptype list yields a list_del write into freed memory when the hook is later removed, a controllable write primitive typical of use-after-free exploitation.
- A:HAvailability impact, high
- The re-added hook makes netdev_run_todo() hit BUG_ON(!list_empty(&dev->ptype_all)) while RTNL is held, oopsing the kernel and permanently wedging all further network configuration — a repeatable, unprivileged host-wide denial of service.