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CVE-2026-72393
eth: fbnic: don't cache shinfo across skb realloc
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72393 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| 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
fbnic_tx_lso() calls skb_cow_head() which may reallocate the skb including the shared info. We can't use the pointer calculated before the call. BUG: KASAN: slab-use-after-free in fbnic_tx_lso.isra.0+0x668/0x8e0 Read of size 4 at addr ff110000262edd98 by task swapper/5/0 Call Trace: fbnic_tx_lso.isra.0+0x668/0x8e0 fbnic_xmit_frame+0x622/0xba0 dev_hard_start_xmit+0xf4/0x620 Allocated by task 8653: __alloc_skb+0x11e/0x5f0 alloc_skb_with_frags+0xcc/0x6c0 sock_alloc_send_pskb+0x327/0x3f0 __ip_append_data+0x188b/0x47a0 ip_make_skb+0x24a/0x300 udp_sendmsg+0x14d2/0x21e0 Freed by task 0: kfree+0x123/0x5a0 pskb_expand_head+0x36c/0xfa0 fbnic_tx_lso.isra.0+0x500/0x8e0 fbnic_xmit_frame+0x622/0xba0 dev_hard_start_xmit+0xf4/0x620 sch_direct_xmit+0x25b/0x1100 The buggy address belongs to the object at ff110000262edc40 which belongs to the cache skbuff_small_head of size 640 The buggy address is located 344 bytes inside of freed 640-byte region [ff110000262edc40, ff110000262ede
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/ethernet/meta/fbnic/fbnic_txrx.c
- What this is
- META ETHERNET DRIVERSMAINTAINERS section matched on drivers/net/ethernet/meta/ · Maintained
Check it on the machine
grep -wE 'CONFIG_ETHERNET|CONFIG_FBNIC|CONFIG_NET_VENDOR_META' /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.
Show whether Debian builds this, per release
Debian does not build this code in 3 releases. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sidn
- ?
- not established - no Makefile entry for the affected file
- n
- not enabled on any flavour - this release does not build the code
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 switches
- CONFIG_ETHERNET, CONFIG_FBNIC, CONFIG_NET_VENDOR_META
- 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
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.63%, higher than 49.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.15 | 6.18.40 | 83df3e2594cd |
| 6.15 | 7.1.5 | 21f304c2aae4 |
| 6.15 | 7.2 | 62b68b774f06 |
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 in fbnic_tx_lso on the outbound netdev path; KASAN shows udp_sendmsg→ip_make_skb→dev_hard_start_xmit. Remote peers can trigger GSO/USO/TSO transmits on internet-facing Meta hosts with fbnic (TCP responses or UDP USO), reaching the vulnerable driver without local access.
- AC:LAttack complexity, low
- The USO selftest reliably reproduces the UAF when sending UDP_SEGMENT GSO skbs; attackers control MSS, payload size, and timing to force skb_cow_head/pskb_expand_head to reallocate the skb, making the stale shinfo dereference repeatable rather than dependent on uncontrollable state.
- PR:NPrivileges required, none
- Triggering requires only standard unprivileged socket sendmsg with GSO/USO offload on a host using fbnic, or causing such outbound segmented traffic as an unauthenticated remote client; no CAP_NET_ADMIN, root, or special credentials are needed along the traced path.
- UI:NUser interaction, none
- Exploitation is fully attacker-driven through crafted network traffic or socket operations; no victim click, mount, or other voluntary action is required beyond normal always-on network service operation.
- S:UScope, unchanged
- Impact is kernel slab corruption and crash/privilege escalation within the host kernel security domain; it does not cross a VM/hypervisor or IOMMU boundary into a separate security authority.
- C:HConfidentiality impact, high
- KASAN reports a slab use-after-free with a 4-byte read from freed skb_shared_info after pskb_expand_head; UAF of shinfo fields (gso_type, gso_size, gso_segs) enables heap grooming and arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- Use-after-free of skb_shared_info in the transmit LSO path is memory corruption in attacker-influenced heap objects; stale shinfo values drive metadata and checksum updates, enabling control of kernel data and potential code execution primitives.
- A:HAvailability impact, high
- The reported KASAN slab-use-after-free in fbnic_tx_lso causes kernel oops/panic on transmit; repeated GSO/USO/TSO packets can crash or hang the system, denying availability on affected fbnic-equipped servers.