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CVE-2026-74724
ipvs: avoid out-of-bounds write in ip_vs_nat_icmp
Published 2026-08-22 (2 months 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-2026-74724 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 | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Sashiko warns that local attacker can modify the packet while it is processed by IPVS. Some places read the IP ihl field multiple times which can cause out-of-bounds access. One such place is ip_vs_nat_icmp where we can write after the validated area. Fix it by providing ciph argument just like it is done for IPv6 and use ciph->len as offset to the embedded transport header. Modify some IPv4 header checks by reading the ihl field only once.
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_vs.h
net/netfilter/ipvs/ip_vs_core.c
net/netfilter/ipvs/ip_vs_xmit.c
- What this is
- IPVSMAINTAINERS section matched on include/net/ip_vs.h · 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, sid, bookworm · linux-6.12m
- 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
- 2026-08-22 (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
- 0.12%, higher than 1.9% 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 |
|---|---|---|
| 2.6.12 | 6.1.183 | 3b8f79af0e98 |
| 2.6.12 | 6.6.152 | 3c779b258c9c |
| 2.6.12 | 6.12.104 | be65fa324640 |
| 2.6.12 | 6.18.45 | a69a4b3fff58 |
| 2.6.12 | 7.1.9 | 243d0187ec4c |
| 2.6.12 | 7.2 | 646922a03794 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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
- The OOB write in ip_vs_nat_icmp() requires a local process to change the embedded IPv4 ihl in skb frags between ip_vs_fill_iph_skb_icmp() validation and the NAT write; remote-only ICMP to IPVS netfilter hooks cannot perform that TOCTOU without local access to the packet buffer.
- AC:LAttack complexity, low
- A local attacker controls both sides of the race by concurrently injecting ICMP errors with TCP/UDP/SCTP payloads matching an IPVS NAT connection and modifying the embedded header ihl in skb frags during softirq processing; no victim-specific state or uncontrollable heap layout is required.
- PR:LPrivileges required, low
- Triggering requires a local account able to race skb frag modification (e.g., via raw/packet sockets with CAP_NET_RAW, obtainable in a user namespace) against IPVS ICMP NAT handling on a host where IPVS is already configured; no init-namespace root is needed.
- UI:NUser interaction, none
- No victim user interaction is required; exploitation is driven entirely by attacker-controlled local packet injection and concurrent frag modification while IPVS processes ICMP errors on NAT-mode connections through LOCAL_IN, LOCAL_OUT, or FORWARD hooks.
- S:UScope, unchanged
- The out-of-bounds write corrupts kernel skb memory on the IPVS load-balancer host within the same kernel security authority; it does not cross VM, container, or IOMMU boundaries into a separate security scope.
- C:HConfidentiality impact, high
- Writing TCP/UDP/SCTP port fields and running ip_send_check() using a re-read inflated ihl corrupts skb data beyond the validated region; out-of-bounds kernel memory corruption is exploitable for information disclosure and heap layout control.
- I:HIntegrity impact, high
- The bug is an out-of-bounds write of 16-bit port values (and checksum updates over an attacker-inflated header length) past skb_ensure_writable()'s bound, enabling adjacent kernel memory corruption and potential control-flow hijacking on internet-facing IPVS NAT nodes.
- A:HAvailability impact, high
- Corrupting skb header memory beyond the ensured writable area can cause kernel oops or panic during ICMP NAT mangling; a local attacker can repeatedly trigger the race on kube-proxy IPVS nodes and hardware load balancers running IPVS NAT mode.