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CVE-2026-74475
vxlan: use neigh_ha_snapshot() in route_shortcircuit()
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74475 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 | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. 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
The neighbour hardware address n->ha can be updated asynchronously by the neighbour subsystem, protected by n->ha_lock seqlock. Reading n->ha without holding the seqlock loop can lead to torn reads or reading a partially updated MAC address. Use neigh_ha_snapshot() in route_shortcircuit() to safely copy n->ha under read_seqbegin()/read_seqretry() lock protection before using it. Note that arp_reduce() and neigh_reduce() seem to have the same issue left for future patches.
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.
drivers/net/vxlan/vxlan_core.c
- What this is
- NETWORKING DRIVERSMAINTAINERS section matched on drivers/net/ · netdev@vger.kernel.org · Maintained
- Kernel module
- vxlan
Check it on the machine
grep -w CONFIG_VXLAN /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 vxlanPrints 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 switch
- CONFIG_VXLAN
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
- 10.0 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:Lsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.45%, higher than 38.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 3.8 | 5.10.265 | 32a9590a8d30 |
| 3.8 | 5.15.216 | d0993fc053f2 |
| 3.8 | 6.1.183 | 87210054bad8 |
| 3.8 | 6.6.151 | d08e8ac13f2e |
| 3.8 | 6.12.103 | ec341bb76d77 |
| 3.8 | 6.18.44 | ff89415d34c3 |
| 3.8 | 7.1.8 | 05f2987f73da |
| 3.8 | 7.2 | 8eca411347e1 |
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:NAttack vector, network
- route_shortcircuit() runs on the vxlan_xmit() transmit path when overlay IP/IPv6 traffic is encapsulated; in cloud/SDN VTEP deployments a remote tenant can drive dev_queue_xmit() through bridge/IP forwarding without any local syscall or netlink access.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by concurrently sending overlay traffic that hits route_shortcircuit() and generating neighbour ha updates (ARP/NDP churn); repeated attempts do not depend on victim state or uncontrollable memory layout.
- PR:NPrivileges required, none
- Exploitation requires only the ability to send overlay/underlay packets to a VTEP that already has VXLAN_F_RSC and router FDB entries configured by infrastructure; no CAP_NET_ADMIN, root, or host credentials are needed on the victim.
- UI:NUser interaction, none
- Triggering is automatic during kernel packet forwarding and VXLAN encapsulation once matching traffic flows; no mount, file open, or other victim action is required beyond normal overlay operation.
- S:CScope, changed
- A torn n->ha read can rewrite the skb Ethernet destination and reselect a different FDB remote, mis-encapsulating traffic to an unintended VXLAN peer and crossing intended multi-tenant overlay segmentation boundaries beyond the local VTEP authority.
- C:HConfidentiality impact, high
- Unsynchronized reads of neighbour ha during concurrent updates yield torn MAC values that drive post-rewrite FDB lookup and encapsulation, potentially delivering other tenants' overlay frames to an attacker-controlled remote endpoint or leaking mixed neighbour state.
- I:HIntegrity impact, high
- The corrupted hardware address is copied into the skb Ethernet header and steers subsequent vxlan_find_mac_tx()/vxlan_xmit_one() encapsulation, enabling deterministic overlay traffic redirection or injection toward an attacker-chosen VTEP rather than the intended router destination.
- A:LAvailability impact, low
- While the host kernel does not panic, torn MAC rewriting can cause mis-encapsulation, FDB misses, and dropped or misdelivered overlay packets, producing intermittent connectivity loss and performance degradation on affected VTEP nodes under sustained attack.