CVE-2026-64048 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
net/smc: reject CHID-0 ACCEPT that matches an empty ism_dev slot
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.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability exists in the Linux kernel's SMC-D (Shared Memory Communications - Direct) implementation where a race condition and improper validation allows for a null pointer dereference during connection establishment. The issue stems from how the SMC-D client handles device slot management, specifically with the reserved slot 0 that is intended for SMC-Dv1 devices while V2 entries begin at index 1. When no V1 device is selected, slot 0 remains in its initialized state with ism_dev[0] set to NULL and ism_chid[0] set to 0, creating an exploitable condition where a malicious peer can craft a response that matches this empty slot.
The technical flaw occurs in the smc_v2_determine_accepted_chid() function which iterates through the ism_dev array starting from index 0 using only the CHID value for matching. Since the empty slot 0 has chid == 0, a malicious peer can send a response with d1.chid == 0 that correctly matches this empty entry. This causes the system to incorrectly set ini->ism_selected = 0, bypassing proper validation checks that should ensure a valid device reference exists before accepting the connection. The vulnerability is classified as a null pointer dereference under CWE-476 and represents a classic improper input validation issue that can be exploited through crafted network traffic.
The operational impact of this vulnerability is severe as it allows for kernel memory corruption leading to potential system crashes or privilege escalation opportunities. When smc_conn_create() attempts to dereference the lgr_lock field at offset 0x68 within the smcd_dev structure, it encounters a null pointer since ism_dev[0] is NULL, causing a kernel oops and potentially allowing attackers to execute arbitrary code with kernel privileges. This vulnerability affects systems running Linux kernels with SMC-D support and can be exploited remotely through network-based attacks targeting the SMC protocol implementation. The attack vector aligns with ATT&CK technique T1068 (Exploitation for Privilege Escalation) and T1210 (Exploitation of Remote Services).
The fix implemented requires adding a validation check to ensure that ism_dev[i] is non-NULL before accepting any CHID match, preventing the acceptance of connections through empty device slots. This mitigation aligns with security best practices for input validation and defensive programming, ensuring that all references are properly validated before use. The solution directly addresses the root cause by requiring proper device initialization before accepting connection parameters, preventing malicious actors from exploiting the uninitialized state of reserved slots in the SMC-D device management system.