Look up another CVE · open CVE-2026-72418 in the interactive tracker
CVE-2026-72418
netfilter: nf_conncount: prevent connlimit drops for early confirmed ct
Published 2026-08-15 (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-2026-72418 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Commit 69894e5b4c5e ("netfilter: nft_connlimit: update the count if add was skipped") introduced a regression where packets for valid connections are dropped when using connlimit for soft-limiting scenarios. The issue occurs when a new connection reuses a socket currently in the TIME_WAIT state. In this scenario, the connection tracking entry is evaluated as already confirmed. Previously, __nf_conncount_add() assumed that if a connection was confirmed and did not originate from the loopback interface, it should skip the addition and return -EEXIST. Skipping the addition triggers a garbage collection run that cleans up the TIME_WAIT connection. Consequently, the active connection count drops to 0, which xt_connlimit mishandles, leading to the false rejection of the perfectly valid new connection. Fix this by replacing the interface check with protocol-agnostic state checks. We now skip the tree insertion and preserve the lockless garbage collection optimization only if the connection is IPS_ASSURED. This allows early-confirmed setup packets (such as reused TIME_WAIT sockets or locally generated SYN-ACKs) to be properly evaluated and counted without falsely dropping. The goto check_connections path is maintained to ensure these setup packets are deduplicated correctly. This has been tested with slowhttptest and HTTP server configured locally to ensure we are not breaking soft-limiting scenarios for local or external connections. In addition, it was tested with a OVS zone limit too.
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_conncount.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nf_conncount
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NETFILTER_CONNCOUNT' /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_conncountPrints 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_NETFILTER_CONNCOUNT
- 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
- 2026-08-15 (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
- 0.72%, higher than 52.9% 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 |
|---|---|---|
| 5.10.248 | 5.10.261 | 000ac6830b56 |
| 5.15.198 | 5.15.212 | cbe2d14a7c5b |
| 6.1.160 | 6.1.178 | 3793d24de224 |
| 6.6.120 | 6.6.145 | abef7f817217 |
| 6.12.63 | 6.12.97 | ebfe8249ba79 |
| 6.18.2 | 6.18.40 | 329f2626ee5c |
| 6.19 | 7.1.5 | be52572c6d55 |
| 6.19 | 7.2 | c8b6f36f7669 |
| 6.17.13 | 0 | 0 |
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
- Exploitation is triggered by remote TCP packets processed through netfilter INPUT/FORWARD hooks (xt_connlimit, nft_connlimit, OVS ct-limit) that call nf_conncount_count_skb() on received skbs; no local syscall or ioctl is required.
- AC:LAttack complexity, low
- An unauthenticated remote attacker can reliably trigger the bug by rapidly reconnecting to reuse a TIME_WAIT 4-tuple, a normal TCP behavior they fully control; no race against unrelated system events is required.
- PR:NPrivileges required, none
- The attacker needs no privileges on the victim host; only inbound network access to a service protected by admin-configured connlimit rules is required, and no CAP_NET_ADMIN or namespace capabilities are needed to trigger the faulty counting path.
- UI:NUser interaction, none
- No victim user action is required; exploitation is achieved solely by sending crafted connection patterns over the network to a host already running connlimit enforcement.
- S:UScope, unchanged
- Impact is confined to incorrect netfilter connection accounting and packet drops within the same kernel/network security domain; there is no cross-boundary escape such as VM breakout or privilege escalation.
- C:NConfidentiality impact, none
- The flaw is a connection-count bookkeeping error and premature garbage collection; it does not read kernel memory, leak data, or involve any memory corruption primitive.
- I:NIntegrity impact, none
- No unauthorized modification of data or code occurs; the only effect is dropping or mis-evaluating packets against connlimit policy, which is an availability concern rather than integrity compromise.
- A:HAvailability impact, high
- When the miscount drives the connection count to zero, xt_connlimit hot-drops valid packets, falsely rejecting legitimate new connections and causing repeatable denial of service against protected services without authentication.