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CVE-2026-74624
netfilter: nf_conntrack: defer invalid log until after unlock
Published 2026-08-22 (2 months 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-2026-74624 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
TCP and SCTP conntrack paths can emit invalid-packet logs while ct->lock is still held. When invalid logging is routed to nfnetlink_log and conntrack export is enabled, the log path can re-enter conntrack netlink glue and dump the same conntrack again. Protocol attribute dumping may take ct->lock, so logging while holding that lock can deadlock. Defer the TCP invalid logs by storing only the minimal log context while ct->lock is held and emitting the log after unlocking. Also make the TCP timeout-lowering invalid path return whether a log is needed, then emit that log after unlocking. Do the same for the SCTP invalid state-transition log that can be reached while ct->lock is held. Add a lockdep assertion to nf_ct_l4proto_log_invalid() so future callers that log invalid conntracks while holding ct->lock are caught outside TCP and SCTP as well.
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_conntrack_proto.c
net/netfilter/nf_conntrack_proto_sctp.c
net/netfilter/nf_conntrack_proto_tcp.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nf_conntrack
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NF_CONNTRACK' /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_conntrackPrints 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_CONNTRACK
- 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
- net/netfilter
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.1 | 6.1.184 | ca97360eba4b |
| 6.1 | 6.6.152 | 63853eb20bba |
| 6.1 | 6.12.104 | 9480fcf70a5a |
| 6.1 | 6.18.45 | 0424186d570a |
| 6.1 | 7.1.9 | c0224327b7cb |
| 6.1 | 7.2 | 2d19b95c9723 |
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
- The flaw is hit in nf_conntrack_tcp_packet()/nf_conntrack_sctp_packet() from the NF_INET_PRE_ROUTING and LOCAL_OUT netfilter hooks on received or forwarded TCP/SCTP traffic, so a remote peer can trigger invalid conntrack handling with crafted packets to internet-facing NAT gateways, routers, and servers.
- AC:LAttack complexity, low
- Once nf_conntrack_log_invalid, nflog binding, and NFULNL_CFG_F_CONNTRACK are enabled (the CVE-scoped configuration on monitored firewalls), an attacker deterministically deadlocks by sending invalid-sequence TCP or invalid-state SCTP packets on tracked flows without races or special memory layout.
- PR:NPrivileges required, none
- Triggering the vulnerable conntrack path requires only the ability to send TCP/SCTP packets to a host already running connection tracking with invalid logging; no local account, CAP_NET_ADMIN, or netlink configuration privileges are needed on the attacker side.
- UI:NUser interaction, none
- Exploitation is driven entirely by network packet delivery and softirq packet processing; no victim must open files, mount filesystems, or perform any interactive action beyond normal network connectivity to the target.
- S:UScope, unchanged
- The deadlock confines impact to the same kernel networking authority processing the packet; it does not cross VM, container, or IOMMU boundaries to compromise a separate security domain.
- C:NConfidentiality impact, none
- This is a recursive spinlock deadlock in conntrack invalid logging with no memory corruption, out-of-bounds access, use-after-free, or information-disclosure primitive.
- I:NIntegrity impact, none
- The bug causes a lock re-entry hang during logging only; it does not modify kernel or user data, provide arbitrary write primitives, or enable code execution.
- A:HAvailability impact, high
- Re-acquiring ct->lock while it is held deadlocks packet processing on the affected CPU in softirq context, can stall networking on that core, and may escalate to soft lockup or watchdog-induced kernel panic under sustained attack.