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CVE-2026-98320
netfilter: flowtable: hold reference on ct until flow is released
Published 2026-10-06 (13 days ago) by the Linux kernel CNA. Subsystem net/netfilter. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-98320 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-6568-1 · 2026-10-16 · text | 6.12.113-1 | Update the kernel and reboot. DSA-6568-1 shipped the fix on 2026-10-16, in 6.12.113-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
nf_ct_put() releases the ct->ext area inmediately, the rcu typesafe semantics also allow to refer to the wrong conntrack from the flowtable datapath. Hold reference on ct until flow is released after rcu grace period. Add rcu_barrier() on module exit path, to ensure pending flow entries are release before module goes away.
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/netfilter/nf_flow_table_core.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nf_flow_table
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NF_FLOW_TABLE' /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 nf_flow_tablePrints 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 as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NETFILTER, CONFIG_NF_FLOW_TABLE
- 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
- 2026-10-06 (13 days 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
- 0.14%, higher than 2.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/netfilter
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.16 | 5.10.271 | 93ff1594be1a |
| 4.16 | 5.15.222 | eed6997e8dc4 |
| 4.16 | 6.1.189 | 61c6688be282 |
| 4.16 | 6.6.158 | a43cd2b67b91 |
| 4.16 | 6.12.112 | 8274cdc5f9c5 |
| 4.16 | 6.18.54 | 12c1ac230f4c |
| 4.16 | 7.2.8 | d9e6175a3ee4 |
| 4.16 | 7.3 | e75a9fa1d44b |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DSA-6568-1 | 2026-10-16 | trixie 6.12.113-1 | 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:LAttack vector, local
- The freed ct is reached from nf_flow_offload_forward() (nf_ct_acct_update/flow_offload_teardown on flow->ct) but freeing it needs the conntrack killed (nf_ct_is_dying) and flow_offload_del() run; a remote peer only supplies forwarded packets and cannot kill an offloaded ct, so the full trigger needs local nftables/ctnetlink access.
- AC:LAttack complexity, low
- The attacker drives every side of the race: they flood packets through their own flowtable, delete the ct via ctnetlink, and force nf_flow_offload_gc_step()->flow_offload_del() at once by downing the veth (nf_flow_table_gc_cleanup flush_delayed_work). The window is narrow but can be retried indefinitely.
- PR:LPrivileges required, low
- Creating the nftables flowtable, adding veth forwarding and sending IPCTNL_MSG_CT_DELETE need only CAP_NET_ADMIN in a network namespace, which an unprivileged user gets via unshare -Urn.
- UI:NUser interaction, none
- No victim action is needed; the attacker sets up the flowtable, the traffic and the conntrack/flow teardown entirely within their own namespace.
- S:UScope, unchanged
- Memory corruption in the host kernel's netfilter flowtable/conntrack objects yields kernel privilege escalation within the same authority; no VM or hardware boundary is crossed.
- C:HConfidentiality impact, high
- flow_offload_free() dropped the ct reference before the RCU grace period, so in-flight readers dereference ct->ext after nf_conntrack_free() has kfree'd it, or a recycled SLAB_TYPESAFE_BY_RCU nf_conn now owned by another connection - a use-after-free that can be groomed to leak kernel memory.
- I:HIntegrity impact, high
- The stale reader writes freed or reused memory: nf_ct_acct_add() does atomic64_add into the freed ct->ext counters, and flow_offload_teardown()/flow_offload_fixup_ct() modify status/timeout of a recycled conntrack, giving heap-corruption primitives.
- A:HAvailability impact, high
- The use-after-free on ct->ext and recycled nf_conn objects in the forwarding softirq can corrupt the slab and crash the kernel.