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CVE-2026-64048
net/smc: reject CHID-0 ACCEPT that matches an empty ism_dev slot
Published 2026-07-19 (3 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-2026-64048 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 | fixed | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
On the SMC-D client, slot 0 of ini->ism_dev[]/ini->ism_chid[] is reserved for an SMC-Dv1 device. smc_find_ism_v2_device_clnt() populates V2 entries starting at index 1, so when no V1 device is selected slot 0 is left in its kzalloc()'ed state with ism_dev[0] == NULL and ism_chid[0] == 0. smc_v2_determine_accepted_chid() then matches the peer's CHID against the array starting from index 0 using the CHID alone. A malicious peer replying to a SMC-Dv2-only proposal with d1.chid == 0 matches the empty slot, ini->ism_selected becomes 0, and the subsequent ism_dev[0]->lgr_lock dereference in smc_conn_create() faults at offsetof(struct smcd_dev, lgr_lock) == 0x68: BUG: KASAN: null-ptr-deref in _raw_spin_lock_bh+0x79/0xe0 Write of size 4 at addr 0000000000000068 by task exploit/144 Call Trace: _raw_spin_lock_bh smc_conn_create (net/smc/smc_core.c:1997) __smc_connect (net/smc/af_smc.c:1447) smc_connect (net/smc/af_smc.c:1720) __sys_connect __x64_sys_connect do_syscall_64 Require ism_dev[i] to be non-NULL before accepting a CHID match.
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/af_smc.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 2 releases, so the answer depends on which release the machine runs.
- bookworm, trixiem
- forky, sidn
- 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
- 2026-07-19 (3 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.50%, higher than 41.6% 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 |
|---|---|---|
| 5.10 | 5.10.266 | 903f7688ffeb |
| 5.10 | 5.15.217 | dd2f9dd83c68 |
| 5.10 | 6.1.175 | 6927cacf2b10 |
| 5.10 | 6.6.142 | d38ba387244e |
| 5.10 | 6.12.92 | 53eb7bd09aac |
| 5.10 | 6.18.34 | afa9036b8c99 |
| 5.10 | 7.0.11 | 65edb3b0822c |
| 5.10 | 7.1 | 277740023def |
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 fault is triggered while processing a malicious CLC ACCEPT message received from a remote TCP peer during the SMC-D handshake; the attacker controls the server response over the network.
- AC:LAttack complexity, low
- Once a victim with SMC-Dv2 hardware initiates an SMC connection, a malicious peer can reliably send `d1.chid == 0` in the CLC ACCEPT to match the empty reserved slot 0 without races or special timing.
- PR:NPrivileges required, none
- No local privileges are required on the victim host; an unauthenticated remote attacker operating a malicious SMC server can crash connecting clients, and unprivileged users can create SMC sockets without capability checks.
- UI:NUser interaction, none
- Exploitation requires only that a victim application initiate a normal outbound SMC connection to the attacker's server, which occurs automatically in enterprise middleware without per-connection user action.
- S:UScope, unchanged
- The vulnerability causes a kernel crash on the victim host but does not cross a security boundary such as VM escape or sandbox breakout.
- C:NConfidentiality impact, none
- The bug is a null pointer dereference when taking `ism_dev[0]->lgr_lock`; it causes an immediate kernel fault with no information disclosure.
- I:NIntegrity impact, none
- The attempted write at address 0x68 is a spinlock operation on a NULL `smcd_dev` pointer, not a controlled or arbitrary memory modification primitive.
- A:HAvailability impact, high
- A successful trigger causes a kernel null pointer dereference (KASAN-reported oops/panic), crashing the affected system or at minimum the connecting process's kernel context.