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CVE-2026-74493
net/smc: fix socket use-after-free during link group termination
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/smc. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74493 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
__smc_lgr_terminate() drops conns_lock after finding a connection in lgr->conns_all, but before taking a reference on its socket. The connection is embedded in the socket, and its registration reference protects it only while the connection remains in the tree. A concurrent close can unregister the connection and drop that reference, freeing the socket before the termination worker reaches sock_hold(). The race is reachable when close overlaps link group termination. Local stress testing reproduced the use-after-free and KASAN reported: BUG: KASAN: slab-use-after-free in __smc_lgr_terminate.part.0 [smc] Write of size 4 by task kworker/3:3 Workqueue: events smc_lgr_terminate_work [smc] __smc_lgr_terminate.part.0 [smc] The socket was allocated by smc_create(), freed through slab_free_after_rcu_debug(), and was followed by: refcount_t: addition on 0; use-after-free. __smc_lgr_terminate.part.0 [smc] Take the socket reference while conns_lock still protects the tree entry. The unregister path then cannot drop the last reference until termination has finished using the socket.
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.
net/smc/smc_core.c
- What this is
- SHARED MEMORY COMMUNICATIONS (SMC) SOCKETSMAINTAINERS section matched on net/smc/ · linux-rdma@vger.kernel.org · Supported
- Kernel module
- smc
Check it on the machine
grep -w CONFIG_SMC /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 smcPrints 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 does not build this code in 2 releases. It does build it in 3 releases, so the answer depends on which release the machine runs.
- bookworm, trixiem
- forky, sidn
- bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- n
- not enabled on any flavour - this release does not build the code
- Build switch
- CONFIG_SMC
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
- 0.50%, higher than 41.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/smc
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.5 | 5.10.265 | ff44f2df57fb |
| 5.5 | 5.15.216 | 9fb17c95b8f0 |
| 5.5 | 6.1.183 | bea8dc14de2d |
| 5.5 | 6.6.151 | 5a42f162b857 |
| 5.5 | 6.12.103 | 281c103a8eae |
| 5.5 | 6.18.44 | f807a63d0d95 |
| 5.5 | 7.1.8 | f0541a775d04 |
| 5.5 | 7.2 | f621d6ebeebb |
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 in __smc_lgr_terminate() when a link group shuts down; that path is driven by SMC LLC control messages from a remote peer over RoCE/RDMA (smc_llc_rx_handler), including DELETE_LINK_ALL and protocol-violation termination, not only local syscalls.
- AC:LAttack complexity, low
- An SMC peer can overlap link-group termination with connection teardown by sending DELETE_LINK_ALL (or a terminating LLC event) while aborting/closing the same session; the fix report shows reliable stress reproduction, and the attacker controls both sides of the terminate/close race.
- PR:NPrivileges required, none
- Exploitation needs only completing an SMC handshake as a network peer to the victim; no local account, capabilities, or namespace admin rights on the victim host are required beyond normal remote connectivity to the SMC service.
- UI:NUser interaction, none
- No victim user action is needed; a remote peer can trigger termination and concurrent connection teardown purely through kernel protocol handling, without the user mounting filesystems, opening files, or performing other interactive steps.
- S:UScope, unchanged
- The impact stays within the host kernel boundary (memory corruption and potential local privilege escalation) and does not cross VM, container, or IOMMU security authorities into another trust domain.
- C:HConfidentiality impact, high
- KASAN reported slab-use-after-free in __smc_lgr_terminate with refcount_t addition on 0 during sock_hold() on a freed smc_sock; UAF on kernel heap objects can be turned into arbitrary kernel memory disclosure via heap grooming.
- I:HIntegrity impact, high
- The UAF is a write of size 4 to freed socket memory during sock_hold(), giving a kernel heap corruption primitive that can be developed into arbitrary write or control-flow hijack for kernel code execution.
- A:HAvailability impact, high
- The reported UAF occurs in the smc_lgr_terminate workqueue and can crash the kernel (oops/panic); repeated remote triggering against SMC/RoCE services can also cause sustained denial of service.