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CVE-2026-72157
net: thunderbolt: Fix frags[] overflow by bounding frame_count
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-2026-72157 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
tbnet_poll() assembles a multi-frame ThunderboltIP packet into one skb. The first frame goes into the skb linear area and every further frame is added as a page fragment. skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, hdr_size, frame_size, TBNET_RX_PAGE_SIZE - hdr_size); A packet of frame_count frames therefore ends up with frame_count - 1 fragments. tbnet_check_frame() only bounds the peer supplied frame_count to TBNET_RING_SIZE / 4 (64), which is far above MAX_SKB_FRAGS (17 by default). A peer that sends a packet of 19 or more small frames pushes nr_frags past MAX_SKB_FRAGS, so skb_add_rx_frag() writes past skb_shinfo()->frags[] and corrupts memory after the shared info. Tighten the start of packet bound to MAX_SKB_FRAGS + 1 so a packet can never produce more fragments than frags[] can hold. This matches the recent skb frags overflow fixes in other receive paths, for example f0813bcd2d9d ("net: wwan: t7xx: fix potential skb->frags overflow in RX path") and 600dc40554dc ("net: usb: cdc-phonet: fix skb frags[] overflow in rx_complete()").
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/thunderbolt/main.c
- What this is
- THUNDERBOLT NETWORK DRIVERMAINTAINERS section matched on drivers/net/thunderbolt/ · netdev@vger.kernel.org · Maintained
- Kernel module
- thunderbolt_net
Check it on the machine
grep -w CONFIG_USB4_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 thunderbolt_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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixieMnot built on amd64/cloud-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidMnot built on amd64/cloud-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- ?
- not established - no Makefile entry for the affected file
- M
- a module where it is built at all; some flavours do not build it
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switch
- CONFIG_USB4_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
- 2026-08-15 (2 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- adjacent network (AV:A)source
- EPSS
- 0.34%, higher than 26.4% 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 |
|---|---|---|
| 4.15 | 5.10.266 | f96b3b35c622 |
| 4.15 | 5.15.217 | 6262f51e09d8 |
| 4.15 | 6.1.184 | 569ba39b2d12 |
| 4.15 | 6.6.145 | 2b3b4e5ff5a5 |
| 4.15 | 6.12.97 | e27beb4536cb |
| 4.15 | 6.18.40 | e5824d5b841d |
| 4.15 | 7.1.5 | fe6b606fbf0c |
| 4.15 | 7.2 | 55d9895f8997 |
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:AAttack vector, adjacent network
- The flaw is triggered by malicious ThunderboltIP frames sent from a peer on the same direct Thunderbolt/USB4 link; exploitation is not Internet-routable but is reachable from an adjacent connected host, dock, or peripheral without local syscall access.
- AC:LAttack complexity, low
- An adjacent peer can reliably trigger the overflow by sending a start-of-packet header with frame_count of 19-64 and delivering the matching small frames; no races or attacker-uncontrollable heap layout are required.
- PR:NPrivileges required, none
- The attacker needs no account, capability, or privilege on the victim OS; a malicious Thunderbolt/USB4 peer that completes XDomain ThunderboltIP login can send the crafted RX frames directly over the established DMA path.
- UI:NUser interaction, none
- Once a ThunderboltIP session is active, which is common with docks, direct laptop-to-laptop links, and shared workstations, triggering the bug requires no further victim action beyond the existing link.
- S:UScope, unchanged
- Memory corruption occurs in the kernel Thunderbolt network driver during skb reassembly and does not by itself cross a VM, container, or IOMMU security boundary.
- C:HConfidentiality impact, high
- skb_add_rx_frag() writes past skb_shinfo()->frags[], corrupting adjacent kernel memory; such out-of-bounds skb metadata corruption is reasonably leverageable for information disclosure as well as further exploitation.
- I:HIntegrity impact, high
- The overflow is an attacker-controlled out-of-bounds write of skb fragment descriptors beyond MAX_SKB_FRAGS, which can corrupt heap/skb metadata and be developed into arbitrary kernel memory modification or code execution.
- A:HAvailability impact, high
- Corrupting memory past skb_shared_info can cause kernel oopses, panics, or unstable behavior during RX processing, and repeated malicious packets can deny service on affected systems.