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CVE-2026-68476
ipvs: reload ip header after head reallocation
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-2026-68476 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. 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
__ip_vs_get_out_rt() calls skb_ensure_writable() which may reallocate skb->head.
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/ipvs/ip_vs_xmit.c
- What this is
- IPVSMAINTAINERS section matched on net/netfilter/ipvs/ · netdev@vger.kernel.org · Maintained
- Kernel module
- ip_vs
Check it on the machine
grep -wE 'CONFIG_IP_VS|CONFIG_NETFILTER' /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_vsPrints 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_IP_VS, CONFIG_NETFILTER
- 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
- 0.71%, higher than 52.8% 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 |
|---|---|---|
| 4.10 | 5.10.269 | 4f2d11514215 |
| 4.10 | 5.15.220 | 657118cad620 |
| 4.10 | 6.1.187 | a10f5080afbe |
| 4.10 | 6.6.145 | ac6ac3d35bfc |
| 4.10 | 6.12.97 | e51687fc56c2 |
| 4.10 | 6.18.40 | 3fb7edd2018b |
| 4.10 | 7.1.5 | ad1e14710b36 |
| 4.10 | 7.2 | a2f57827bf7c |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | 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:NAttack vector, network
- The flaw is in ip_vs_bypass_xmit() on the IPVS netfilter receive path (NF_INET_LOCAL_IN/FORWARD); remote IPv4 packets to a configured virtual-server VIP reach ip_vs_in_hook() and ip_vs_leave() without local syscalls or ioctl.
- AC:LAttack complexity, low
- Once cache_bypass is enabled on a fwmark IPVS service with no backend, an attacker can repeatedly send traffic to the VIP; cloned skbs (common with bridging, mirroring, or shared receive buffers) make skb_ensure_writable() reallocate skb->head deterministically.
- PR:NPrivileges required, none
- Exploitation requires only sending IP packets to the load balancer VIP; IPVS/cache_bypass configuration is an operator prerequisite on the target, not a Linux capability the remote attacker must hold.
- UI:NUser interaction, none
- No victim interaction is required; kernel processing of attacker-crafted network packets on the IPVS bypass transmit path alone triggers the stale header pointer use after skb head reallocation.
- S:UScope, unchanged
- Impact is kernel heap corruption and load-balancer compromise within the host kernel security domain; it does not cross VM, container, or IOMMU boundaries to another security authority.
- C:HConfidentiality impact, high
- After pskb_expand_head() frees the old skb->head, ip_send_check() uses the stale iph pointer and ip_fast_csum() reads attacker-influenced bytes from freed kmalloc memory, a classic use-after-free information disclosure primitive.
- I:HIntegrity impact, high
- ip_send_check() writes through the stale iph pointer (zeroing and updating the checksum field) into freed/reallocated slab memory, enabling heap corruption and potential arbitrary kernel write or control-flow hijack primitives.
- A:HAvailability impact, high
- Writing and reading through a stale IP header pointer after skb head reallocation can corrupt adjacent kernel heap objects or dereference freed memory, causing kernel oops, panic, or hang and repeatable denial of service.