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CVE-2026-72249
netfilter: flowtable: use dst in this direction when pushing IPIP header
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-2026-72249 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
When pushing the IPIP header, the route of the other direction is used to calculate the headroom, use the route in this direction. Accessing the other tuple to set the IP source and destination is fine because this tuple does not provide such information to avoid storing redundant information. However, this tuple already provides the dst for this direction, this went unnoticed because this bug affects headroom and iph->frag_off only at this stage.
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 | ecb78fbb03d3 |
| 6.19 | 7.2 | c328b90c17fc |
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 bug is hit in the netfilter flowtable ingress fast path when offloaded TCP/UDP packets are received on bound netdevs and tunnel encapsulation runs; a remote peer can trigger it by sending traffic through an IPIP flow-offload gateway without local access.
- AC:LAttack complexity, low
- After a flow is offloaded (easily created by the attacker's own connections), asymmetric IPIP gateway routing predictably makes the reverse-direction dst underestimate headroom, so skb_cow_head undersizes and skb_push corrupts memory on each matching packet.
- PR:NPrivileges required, none
- The attacker only needs to send network packets that match an established offloaded flow; nftables flowtable/IPIP setup is an administrator deployment precondition, not a privilege the attacker must hold on the target system.
- UI:NUser interaction, none
- No victim user action is required beyond normal network traffic once flow offload is enabled; exploitation is driven entirely by packets the attacker sends to the gateway.
- S:UScope, unchanged
- Impact is confined to kernel heap memory corruption and potential local privilege escalation within the same host; it does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- Undersized headroom lets skb_push write before skb->head, causing out-of-bounds heap corruption that can expose adjacent kernel objects and be leveraged into arbitrary memory disclosure primitives.
- I:HIntegrity impact, high
- The same skb head underflow is a writable heap corruption primitive that can overwrite adjacent allocator metadata or object contents and be developed into arbitrary kernel code execution.
- A:HAvailability impact, high
- Heap corruption from skb_push underflow can immediately kernel oops/panic the system or be triggered repeatedly to deny service on an internet-facing VPN/edge gateway.