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CVE-2026-64552
virtio-net: fix len check in receive_big()
Published 2026-07-27 (3 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-2026-64552 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-4720-1 · 2026-08-05 · text | 6.1.180-1 | Update the kernel and reboot. DLA-4720-1 shipped the fix on 2026-08-05, in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6405-1 · 2026-07-31 · text | 6.12.100-1 | Update the kernel and reboot. DSA-6405-1 shipped the fix on 2026-07-31, 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. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
receive_big() bounds the device-announced length by (big_packets_num_skbfrags + 1) * PAGE_SIZE. That is still too loose: add_recvbuf_big() sets sg[1] to start at offset sizeof(struct padded_vnet_hdr) into the first page, so the chain actually carries hdr_len + (PAGE_SIZE - sizeof(padded_vnet_hdr)) + big_packets_num_skbfrags * PAGE_SIZE bytes -- 20 bytes less than the check allows for the common hdr_len == 12 case. A malicious virtio backend can announce a len in that gap. page_to_skb() then walks one frag past the page chain, storing a NULL page->private into skb_shinfo()->frags[MAX_SKB_FRAGS], which is both an out-of-bounds write past the static frag array and a NULL frag handed up the rx path. Bound len by the size add_recvbuf_big() actually advertised.
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/virtio_net.c
- What this is
- VIRTIO NET DRIVERMAINTAINERS section matched on drivers/net/virtio_net.c · netdev@vger.kernel.org · Maintained
- Kernel module
- virtio_net
Check it on the machine
grep -w CONFIG_VIRTIO_NET /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 virtio_netPrints 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_VIRTIO_NET
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
- 2026-07-27 (3 months ago)source
- CVSS
- 8.4 high
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 3.1% 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 |
|---|---|---|
| 6.1.159 | 6.1.178 | f9451d0fd5ba |
| 6.6.117 | 6.6.145 | 38e94d63e29f |
| 6.12.58 | 6.12.97 | fbeb65154583 |
| 6.18 | 6.18.40 | c7fc9adf4e00 |
| 6.18 | 7.1.5 | e6b8463b7d79 |
| 6.18 | 7.2 | 9e5ad06ea826 |
| 6.17.8 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DLA-4723-1 | 2026-08-07 | bullseye 6.1.180-1~deb11u1 | tracker |
| DLA-4720-1 | 2026-08-05 | bookworm 6.1.180-1 | tracker |
| DSA-6405-1 | 2026-07-31 | trixie 6.12.100-1 | 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 malicious input is the buffer length announced by the virtio backend (hypervisor, vhost-user/VDUSE daemon, or virtio-net hardware device), not data from a network peer; a conforming backend can never announce a length in the vulnerable gap. This is the local device-to-driver attack surface, matching how other malicious-virtio-device bugs are scored.
- AC:LAttack complexity, low
- The backend deterministically controls feature negotiation, MTU (hence big_packets_num_skbfrags), and the announced len, so it can force big-packets mode and hit the 20-byte gap on the first packet with no race or memory-layout luck.
- PR:NPrivileges required, none
- The attacking backend requires no credentials or privileges inside the victim kernel — it is outside the guest's security authority and simply completes an RX descriptor. No guest-side account is needed.
- UI:NUser interaction, none
- Triggered automatically in the NAPI receive path as soon as the backend completes a receive buffer; no victim action is required.
- S:UScope, unchanged
- The corruption and crash are confined to the kernel that owns the virtio-net driver, with no crossing into a different security-managing authority such as an IOMMU or hypervisor boundary.
- C:HConfidentiality impact, high
- A controlled 16-byte out-of-bounds write past skb_shared_info into an adjacent skb head in the NAPI page-frag cache lets the attacker corrupt neighbouring network buffer metadata, which is leverageable to disclose adjacent kernel memory; nr_frags is also left one past MAX_SKB_FRAGS so downstream code reads out-of-bounds frag state.
- I:HIntegrity impact, high
- This is an out-of-bounds write past the end of the static skb_shinfo()->frags[] array with attacker-influenced index and size, corrupting adjacent slab/page-frag memory — per guidance an OOB write is High and is potentially leverageable for control-flow hijack.
- A:HAvailability impact, high
- After the OOB write, a NULL page is stored as a frag and immediately dereferenced via compound_head() in softirq context, producing a guaranteed kernel oops; the backend can repeat this at will.