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CVE-2026-93288
netfilter: nfnetlink_log: wait for rcu grace period before freeing pernet state
Published 2026-09-24 (24 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-2026-93288 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
sashiko reports: "nfnl_log_net_exit() calls nf_log_unset(), which clears the logger pointer without an RCU grace period. Immediately after, ops_free_list() frees the per-net state while concurrent packets might still be executing nf_log_packet() under rcu_read_lock()." Clear the pointer via .pre_exit to make sure rcu readers have completed before pernet storage is free'd. The change in nf_log_syslog.c is only done for consistency: it doesn't use pernet data.
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_log_syslog.c
net/netfilter/nfnetlink_log.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nf_log_syslog
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NF_LOG_SYSLOG' /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_log_syslogPrints 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, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NETFILTER, CONFIG_NF_LOG_SYSLOG
- 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
- 2026-09-24 (24 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
- 0.13%, higher than 2.3% 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 |
|---|---|---|
| 4.12 | 5.15.222 | ba2e246aa294 |
| 4.12 | 6.1.189 | 5570d6c8b320 |
| 4.12 | 6.6.158 | 3b9aa62d78ce |
| 4.12 | 6.12.111 | f44616543745 |
| 4.12 | 6.18.53 | dc20050b6b12 |
| 4.12 | 7.2 | 33d1469b0124 |
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:LAttack vector, local
- The UAF is in nfnl_log_net_exit() (unset moved to nfnl_log_net_pre_exit): cleanup_net() frees nfnl_log_net via ops_free_list() while nf_log_packet()→nfulnl_log_packet() still uses nfnl_log_pernet(). Setup is local NETLINK_NETFILTER nfulnl_recv_config (NFULNL_CFG_CMD_PF_BIND); no remote protocol message carries the bug.
- AC:LAttack complexity, low
- The attacker PF_BINDs nfulnl_logger through nfulnl_recv_config, generates packets that enter nf_log_packet() (conntrack nf_l4proto_log_invalid() while those hooks still exist, or NFLOG), and drops the netns so cleanup_net() races nfnl_log_net_exit()/ops_free_list() against that reader; both sides are attacker-controlled.
- PR:LPrivileges required, low
- nfnetlink_rcv() requires CAP_NET_ADMIN via netlink_net_capable() in sock_net(skb->sk)->user_ns before nfulnl_recv_config can bind the logger; an unprivileged user obtains that capability in a user+net namespace (unshare -Urn).
- UI:NUser interaction, none
- The attacker issues nfulnl_recv_config, injects the logged packets, and destroys their own netns; no victim mount, file open, or other interaction is required.
- S:UScope, unchanged
- The slab UAF of struct nfnl_log_net inside nfulnl_log_packet()/instance_lookup_get_rcu() is host-kernel memory corruption in the same kernel authority, not a VM escape or IOMMU/DMA bypass.
- C:HConfidentiality impact, high
- After ops_free_list() kfree()s the per-net object, nfulnl_log_packet() still calls nfnl_log_pernet() and instance_lookup_get_rcu() walks the freed instance_table hlist, a slab UAF that can be reclaimed for arbitrary kernel reads.
- I:HIntegrity impact, high
- Use-after-free of nfnl_log_net's instance_table and the resulting nfulnl_instance pointer chase (hlist, inst->lock, inst->skb) is a heap UAF write primitive that can hijack control flow.
- A:HAvailability impact, high
- instance_lookup_get_rcu()/nfulnl_log_packet() dereferencing the freed nfnl_log_net can oops or panic the kernel even when the UAF is not turned into a full exploit.