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CVE-2026-74476
veth: convert frag_list skbs before running XDP
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-2026-74476 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
A frag_list skb can reach veth with data_len set but nr_frags zero. veth_convert_skb_to_xdp_buff() only converts skbs that are shared, locked, have frags[], or do not have enough headroom. It later uses skb_is_nonlinear() to decide whether to set XDP_FLAGS_HAS_FRAGS and xdp_frags_size. That exposes frag_list data to XDP as if it were stored in frags[], but frags[] is empty. AF_XDP copy mode can then trust the bogus XDP fragment metadata, walk an empty fragment entry, and crash in memcpy() from __xsk_rcv(). Route non-linear skbs through skb_pp_cow_data() before exposing them to XDP, and only advertise XDP frags when the resulting skb has frags[]. skb_copy_bits() already handles frag_list input, and skb_pp_cow_data() builds frags[] output with skb_add_rx_frag(), which is the representation XDP multi-buffer expects.
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/veth.c
net/core/skbuff.c
- What this is
- NETWORKING DRIVERSMAINTAINERS section matched on drivers/net/ · netdev@vger.kernel.org · Maintained
- Kernel module
- veth
Check it on the machine
grep -w CONFIG_VETH /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 vethPrints 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_VETH
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
- 9.1 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.49%, higher than 40.8% 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 |
|---|---|---|
| 5.18 | 6.1.184 | 0be3632597b8 |
| 5.18 | 6.6.153 | 04958dba44dc |
| 5.18 | 6.12.103 | 5c1c15c540fc |
| 5.18 | 6.18.44 | b24ba0bbffe3 |
| 5.18 | 7.1.8 | f9c1fff857e9 |
| 5.18 | 7.2 | d0d641596304 |
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
- The bug is hit when a received skb traverses veth XDP processing; in cloud/container deployments (e.g. Cloudflare-style edge nodes) remote traffic routed to a veth peer with XDP+AF_XDP can deliver the malformed frag_list skb without local access.
- AC:LAttack complexity, low
- An attacker can reliably supply the required frag_list skb (data_len>0, nr_frags=0) by transmitting from the veth peer via sockets or GRO aggregation, controlling packet size, timing, and content without depending on uncontrollable kernel state.
- PR:NPrivileges required, none
- Remote exploitation needs no attacker privileges when ingress traffic reaches a veth that already has an XDP program redirecting to an AF_XDP socket; only network-delivered skbs trigger veth_convert_skb_to_xdp_buff() and the faulty __xsk_rcv() path.
- UI:NUser interaction, none
- No victim user action is required beyond normal network traffic reaching the veth interface; exploitation is automatic once a qualifying frag_list skb is received and redirected to AF_XDP copy mode.
- S:UScope, unchanged
- The flaw causes kernel memory reads and crashes within the host kernel security boundary; it does not cross VM, hypervisor, or IOMMU isolation boundaries.
- C:HConfidentiality impact, high
- Bogus XDP_FLAGS_HAS_FRAGS metadata makes __xsk_rcv() memcpy from uninitialized frags[] entries via skb_frag_address(), enabling out-of-bounds kernel memory reads into the AF_XDP receive buffer before faulting.
- I:NIntegrity impact, none
- The failure mode is a kernel-side memcpy read using invalid fragment metadata; data is copied into the attacker's AF_XDP ring buffer rather than corrupting kernel or other tenants' memory for integrity purposes.
- A:HAvailability impact, high
- The commit and code path confirm a kernel crash when __xsk_rcv() follows bogus fragment metadata and memcpy faults on an invalid frags[] source address, causing oops/panic and denial of service.