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CVE-2026-72417
netfilter: flowtable: Validate iph->ihl in nf_flow_ip4_tunnel_proto()
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/netfilter. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72417 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| 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
Add sanity check for iph->ihl field in nf_flow_ip4_tunnel_proto() before using it to compute the header size, avoiding out-of-bounds access with malformed IP headers. While at it, use iph->protocol instead of the hardcoded IPPROTO_IPIP constant when setting ctx->tun.proto and reference ctx->tun.hdr_size when updating ctx->offset.
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_ip.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
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.55%, higher than 45.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.19 | 7.1.5 | 025a41e76b51 |
| 6.19 | 7.2 | 84460b644329 |
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_flow_offload_ip_hook on NF_NETDEV_INGRESS for IPv4 packets arriving on nftables flowtable devices; a remote attacker can send crafted malformed IP/IPIP headers to that interface without any local access on the victim.
- AC:LAttack complexity, low
- Once a flowtable ingress hook exists, the attacker fully controls packet headers and can reliably reach nf_flow_ip4_tunnel_proto() by sending IP traffic with an invalid ihl field; no race or victim-specific state beyond admin-enabled flow offload is required.
- PR:NPrivileges required, none
- Exploitation requires no credentials or capabilities on the victim host—only that an administrator previously configured nftables flow offload on an ingress device; any remote sender can deliver the malformed packets to trigger parsing on the fast path.
- UI:NUser interaction, none
- No victim interaction is needed; malicious packets are processed automatically by the netdev ingress netfilter hook during normal receive/forward softirq handling on the configured interface.
- S:UScope, unchanged
- Impact is kernel memory corruption and crashes within the host kernel security boundary; this is standard in-kernel compromise territory, not a VM escape, IOMMU bypass, or other cross-authority scope change.
- C:HConfidentiality impact, high
- Missing ihl validation lets iph->ihl<<2 compute an incorrect header size and ctx->offset, causing out-of-bounds skb reads in subsequent tuple parsing and forwarding; per kernel guidance, OOB reads warrant High confidentiality impact.
- I:HIntegrity impact, high
- Incorrect ctx->offset propagates into nf_flow_tuple_ip() and nf_flow_offload_forward(), which invoke skb_ensure_writable() and perform in-place NAT/header mutation at attacker-influenced offsets—memory corruption exploitable for write primitives warrants High integrity impact.
- A:HAvailability impact, high
- Out-of-bounds access in softirq packet processing on the flowtable fast path can trigger KASAN reports, kernel oops, or panics when malformed headers are processed, constituting High availability impact.