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CVE-2026-72350
netfilter: xt_u32: reject invalid shift counts
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-2026-72350 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
u32_match_it() executes rule-supplied shift operands on a 32-bit value. A malformed u32 rule can provide a shift count of 32 or more, triggering an undefined shift out-of-bounds during packet evaluation. Validate XT_U32_LEFTSH and XT_U32_RIGHTSH operands in u32_mt_checkentry() and reject malformed rules before they reach the packet path.
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/xt_u32.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- xt_u32
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NETFILTER_XT_MATCH_U32' /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 xt_u32Prints 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_XT_MATCH_U32
- 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
- 7.8 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/netfilter
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.23 | 5.10.261 | ca7c92d97012 |
| 2.6.23 | 5.15.212 | b33b44250d57 |
| 2.6.23 | 6.1.178 | 728f479dc044 |
| 2.6.23 | 6.6.145 | 0a8b7a6d7637 |
| 2.6.23 | 6.12.97 | cce42014415c |
| 2.6.23 | 6.18.40 | a597a722fb71 |
| 2.6.23 | 7.1.5 | 00d034fe8230 |
| 2.6.23 | 7.2 | 64cdf7d30ac1 |
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
- Malicious xt_u32 match rules are installed via IPT_SO_SET_REPLACE setsockopt or nftables NFNetlink (nft_compat match); per kernel CNA guidance netfilter/xtables rule setup is Local even though installed rules evaluate on ingress/egress packets through ipt_do_table.
- AC:LAttack complexity, low
- The attacker fully controls XT_U32_LEFTSH/RIGHTSH shift operands (>=32) in matchinfo and can send triggering packets through the hooked netfilter chain; no race or uncontrollable victim state is required.
- PR:LPrivileges required, low
- Installing xt_u32 iptables/nftables rules requires CAP_NET_ADMIN, obtainable by unprivileged users in user/network namespaces via unshare -Urn; ip_tables.c and nfnetlink enforce ns_capable/netlink_net_capable against the namespace user_ns.
- UI:NUser interaction, none
- The attacker installs the malicious u32 match rule and generates matching traffic in their namespace; no separate victim action (opening files, mounting media, clicking links) is needed.
- S:UScope, unchanged
- Undefined shift during xt_u32 packet matching and any resulting kernel crash remain within the host kernel security authority; this is standard local kernel compromise, not a VM escape or sandbox boundary crossing.
- C:HConfidentiality impact, high
- Undefined-behavior shifts on packet-derived u32 values corrupt val and @ offset accumulation, driving attacker-influenced skb_copy_bits reads at unintended offsets; per CNA guidance exploitable kernel memory-unsafe arithmetic warrants High confidentiality.
- I:HIntegrity impact, high
- Invalid shift counts corrupt val/at control flow in the u32_match_it hot path; C11 undefined behavior in kernel netfilter matching is exploitable for integrity compromise and potential code execution per CNA memory-corruption guidance.
- A:HAvailability impact, high
- Evaluating a malformed xt_u32 rule with shift>=32 triggers undefined shift-out-of-bounds during packet matching; vulnerable kernels also BUG() on skb_copy_bits failure, provoking kernel panic/oops during rule evaluation.