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CVE-2026-80978
net: cap advertised IP tunnel headroom
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-80978 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-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
IP tunnel devices derive their advertised needed_headroom from lower output devices. A stack of user-created devices can make the derived value larger than the 16-bit skb header offsets can represent. Once IP output reserves it, skb head expansion can wrap those offsets. The runtime transmit path already caps a growing needed_headroom at 512. Apply the same cap when tunnel configuration publishes needed_headroom derived from a lower output device. Capping the advertised value is safe: IP tunnel transmit still expands the skb when a packet needs more headroom. A nonsensical stacked configuration can therefore incur an extra reallocation, but it cannot publish an unbounded reservation to upper layers.
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.
include/net/ip_tunnels.h
net/ipv4/ip_tunnel.c
net/ipv6/ip6_gre.c
net/ipv6/ip6_tunnel.c
net/ipv6/sit.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on include/net/ip* · netdev@vger.kernel.org · Maintained
- Kernel module
- ip_tunnel
Check it on the machine
grep -wE 'CONFIG_INET|CONFIG_NET_IP_TUNNEL' /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 ip_tunnelPrints 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_INET, CONFIG_NET_IP_TUNNEL
- 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
- 2026-09-11 (37 days 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
- 0.13%, higher than 2.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 3.11 | 5.10.270 | fb889a619723 |
| 3.11 | 5.15.221 | b160422f8103 |
| 3.11 | 6.1.188 | d36e75f56691 |
| 3.11 | 6.6.157 | 84783961cb8b |
| 3.11 | 6.12.109 | bc4e05ae66c9 |
| 3.11 | 6.18.50 | af0ee8f04bea |
| 3.11 | 7.2.4 | 9144f2c53a04 |
| 3.11 | 7.3 | 6b222adeb934 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | 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:LAttack vector, local
- Triggering the wrap requires locally creating a namespace stack of IP tunnel devices (ipip/gre/sit/ip6tnl via rtnetlink or SIOCADDTUNNEL) so bind/link-config can copy an uncapped needed_headroom, then sending packets through that stack. A remote peer cannot build that topology, so the attacker-controlled path is local.
- AC:LAttack complexity, low
- The attacker fully controls tunnel creation, IFLA_IPTUN_LINK/parms.link stacking (or a netkit lower device with a large IFLA_NETKIT_HEADROOM), and the subsequent transmit. Each bind copies lower needed_headroom plus t_hlen until LL_RESERVED_SPACE exceeds 16-bit skb offsets; no race or uninfluenced victim state is required.
- PR:LPrivileges required, low
- Creating and binding these tunnels needs CAP_NET_ADMIN, but rtnetlink uses netlink_ns_capable()/sk_ns_capable() against net->user_ns and ip_tunnel_ctl uses ns_capable(net->user_ns, CAP_NET_ADMIN), so an unprivileged user obtains it with unshare -Urn. Fallback tunl0/ip6tnl0 devices are created in every netns by default.
- UI:NUser interaction, none
- The attacker creates the stacked tunnels and generates the traffic that drives IP output/skb_cow_head; no other user or administrator action is required.
- S:UScope, unchanged
- The resulting skb header-offset wrap corrupts kernel heap in the same OS security authority. This is standard in-kernel privilege escalation, not a VM, IOMMU, or hypervisor boundary crossing.
- C:HConfidentiality impact, high
- After pskb_expand_head adds a >64K nhead, u16 network_header wraps so skb->data points outside skb->head. Neighbour/flow-dissect paths then __skb_pull/read with a negative offset, producing the same unbounded KASAN use-after-free/OOB read as CVE-2024-26804/CVE-2025-40173.
- I:HIntegrity impact, high
- Post-wrap, skb_push/dev_hard_header and iptunnel_xmit/ip6_tnl_xmit write outer IP/GRE headers at the corrupted skb->data, giving an out-of-bounds write into unrelated kernel heap that can be used for control-flow hijacking.
- A:HAvailability impact, high
- The wrapped offsets and subsequent out-of-bounds accesses reliably oops/panic (KASAN, skb_under_panic, or unmapped dereference), matching the confirmed crash impact of the earlier unbounded tunnel-headroom bugs.