CVE-2026-23427

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free in durable v2 replay of active file handles parse_durable_handle_context() unconditionally assigns dh_info->fp->conn to the current connection when handling a DURABLE_REQ_V2 context with SMB2_FLAGS_REPLAY_OPERATION. ksmbd_lookup_fd_cguid() does not filter by fp->conn, so it returns file handles that are already actively connected. The unconditional overwrite replaces fp->conn, and when the overwriting connection is subsequently freed, __ksmbd_close_fd() dereferences the stale fp->conn via spin_lock(&fp->conn->llist_lock), causing a use-after-free. KASAN report: [ 7.349357] ================================================================== [ 7.349607] BUG: KASAN: slab-use-after-free in _raw_spin_lock+0x75/0xe0 [ 7.349811] Write of size 4 at addr ffff8881056ac18c by task kworker/1:2/108 [ 7.350010] [ 7.350064] CPU: 1 UID: 0 PID: 108 Comm: kworker/1:2 Not tainted 7.0.0-rc3+ #58 PREEMPTLAZY [ 7.350068] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 7.350070] Workqueue: ksmbd-io handle_ksmbd_work [ 7.350083] Call Trace: [ 7.350087] <TASK> [ 7.350087] dump_stack_lvl+0x64/0x80 [ 7.350094] print_report+0xce/0x660 [ 7.350100] ? __pfx__raw_spin_lock_irqsave+0x10/0x10 [ 7.350101] ? __pfx___mod_timer+0x10/0x10 [ 7.350106] ? _raw_spin_lock+0x75/0xe0 [ 7.350108] kasan_report+0xce/0x100 [ 7.350109] ? _raw_spin_lock+0x75/0xe0 [ 7.350114] kasan_check_range+0x105/0x1b0 [ 7.350116] _raw_spin_lock+0x75/0xe0 [ 7.350118] ? __pfx__raw_spin_lock+0x10/0x10 [ 7.350119] ? __call_rcu_common.constprop.0+0x25e/0x780 [ 7.350125] ? close_id_del_oplock+0x2cc/0x4e0 [ 7.350128] __ksmbd_close_fd+0x27f/0xaf0 [ 7.350131] ksmbd_close_fd+0x135/0x1b0 [ 7.350133] smb2_close+0xb19/0x15b0 [ 7.350142] ? __pfx_smb2_close+0x10/0x10 [ 7.350143] ? xas_load+0x18/0x270 [ 7.350146] ? _raw_spin_lock+0x84/0xe0 [ 7.350148] ? __pfx__raw_spin_lock+0x10/0x10 [ 7.350150] ? _raw_spin_unlock+0xe/0x30 [ 7.350151] ? ksmbd_smb2_check_message+0xeb2/0x24c0 [ 7.350153] ? ksmbd_tree_conn_lookup+0xcd/0xf0 [ 7.350154] handle_ksmbd_work+0x40f/0x1080 [ 7.350156] process_one_work+0x5fa/0xef0 [ 7.350162] ? assign_work+0x122/0x3e0 [ 7.350163] worker_thread+0x54b/0xf70 [ 7.350165] ? __pfx_worker_thread+0x10/0x10 [ 7.350166] kthread+0x346/0x470 [ 7.350170] ? recalc_sigpending+0x19b/0x230 [ 7.350176] ? __pfx_kthread+0x10/0x10 [ 7.350178] ret_from_fork+0x4fb/0x6c0 [ 7.350183] ? __pfx_ret_from_fork+0x10/0x10 [ 7.350185] ? __switch_to+0x36c/0xbe0 [ 7.350188] ? __pfx_kthread+0x10/0x10 [ 7.350190] ret_from_fork_asm+0x1a/0x30 [ 7.350197] </TASK> [ 7.350197] [ 7.355160] Allocated by task 123: [ 7.355261] kasan_save_stack+0x33/0x60 [ 7.355373] kasan_save_track+0x14/0x30 [ 7.355484] __kasan_kmalloc+0x8f/0xa0 [ 7.355593] ksmbd_conn_alloc+0x44/0x6d0 [ 7.355711] ksmbd_kthread_fn+0x243/0xd70 [ 7.355839] kthread+0x346/0x470 [ 7.355942] ret_from_fork+0x4fb/0x6c0 [ 7.356051] ret_from_fork_asm+0x1a/0x30 [ 7.356164] [ 7.356214] Freed by task 134: [ 7.356305] kasan_save_stack+0x33/0x60 [ 7.356416] kasan_save_track+0x14/0x30 [ 7.356527] kasan_save_free_info+0x3b/0x60 [ 7.356646] __kasan_slab_free+0x43/0x70 [ 7.356761] kfree+0x1ca/0x430 [ 7.356862] ksmbd_tcp_disconnect+0x59/0xe0 [ 7.356993] ksmbd_conn_handler_loop+0x77e/0xd40 [ 7.357138] kthread+0x346/0x470 [ 7.357240] ret_from_fork+0x4fb/0x6c0 [ 7.357350] ret_from_fork_asm+0x1a/0x30 [ 7.357463] [ 7.357513] The buggy address belongs to the object at ffff8881056ac000 [ 7.357513] which belongs to the cache kmalloc-1k of size 1024 [ 7.357857] The buggy address is located 396 bytes inside of [ 7.357857] freed 1024-byte region ---truncated---

CVSS Details

CVSS Score

9.8

Severity

CRITICAL

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:linux:linux_kernel:6.9:-:*:*:*:*:*:* - VULNERABLE

Linux Kernel < 6.8 (Patched in stable branches)

Linux Kernel (ksmbd module enabled)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

# PoC for CVE-2026-23427 (Conceptual)
# Requires impacket library

from impacket.smb3 import SMB3, SMB2_DIALECT_0311
from impacket.smbconnection import SMBConnection
import sys

def trigger_uaf(target_ip, target_port):
    # 1. Establish connection and create file with Durable Handle V2
    try:
        conn = SMBConnection(target_ip, target_ip, sess_port=int(target_port))
        conn.login('guest', '')
        tid = conn.connectTree('share')
        fid = conn.createFile(tid, 'test.txt', desiredAccess=0x2019f, shareAccess=0x7)
        print("[+] File created with handle.")
        
        # 2. Simulate disconnect or specific state to keep handle active
        # In a real scenario, this involves packet manipulation to keep the handle valid
        # while the underlying connection structure is manipulated.
        
        # 3. Send Replay Operation packet
        # This requires raw packet construction to set SMB2_FLAGS_REPLAY_OPERATION
        # and DURABLE_REQ_V2 context to trigger the fp->conn overwrite.
        
        print("[!] Sending malicious replay request to trigger UAF...")
        # Implementation of raw packet sending goes here
        # conn.getSMBServer().sendPacket(malicious_packet)
        
    except Exception as e:
        print(f"[-] Error: {e}")

if __name__ == "__main__":
    trigger_uaf("192.168.1.100", 445)

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-23427
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-23427
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-23427/
[4] VulDB https://vuldb.com/cve/CVE-2026-23427
[5] https://git.kernel.org/stable/c/568a25fd7bcdfb2790f7d42aa2a440dca4435c96
[6] https://git.kernel.org/stable/c/9b0792c3eacf01e67f356d6ef9707b0ae5022419
[7] https://git.kernel.org/stable/c/a5828c14a9e3d5eeed0bcc0a58f0f3fbca0cdcb2
[8] https://git.kernel.org/stable/c/b0158d9d6f4ec5941e49a0b812735db2844f9975
[9] https://git.kernel.org/stable/c/b425e4d0eb321a1116ddbf39636333181675d8f4

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-23427", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-03T16:16:23.797", "lastModified": "2026-04-27T14:16:32.007", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free in durable v2 replay of active file handles\n\nparse_durable_handle_context() unconditionally assigns dh_info->fp->conn\nto the current connection when handling a DURABLE_REQ_V2 context with\nSMB2_FLAGS_REPLAY_OPERATION. ksmbd_lookup_fd_cguid() does not filter by\nfp->conn, so it returns file handles that are already actively connected.\nThe unconditional overwrite replaces fp->conn, and when the overwriting\nconnection is subsequently freed, __ksmbd_close_fd() dereferences the\nstale fp->conn via spin_lock(&fp->conn->llist_lock), causing a\nuse-after-free.\n\nKASAN report:\n\n[ 7.349357] ==================================================================\n[ 7.349607] BUG: KASAN: slab-use-after-free in _raw_spin_lock+0x75/0xe0\n[ 7.349811] Write of size 4 at addr ffff8881056ac18c by task kworker/1:2/108\n[ 7.350010]\n[ 7.350064] CPU: 1 UID: 0 PID: 108 Comm: kworker/1:2 Not tainted 7.0.0-rc3+ #58 PREEMPTLAZY\n[ 7.350068] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014\n[ 7.350070] Workqueue: ksmbd-io handle_ksmbd_work\n[ 7.350083] Call Trace:\n[ 7.350087] <TASK>\n[ 7.350087] dump_stack_lvl+0x64/0x80\n[ 7.350094] print_report+0xce/0x660\n[ 7.350100] ? __pfx__raw_spin_lock_irqsave+0x10/0x10\n[ 7.350101] ? __pfx___mod_timer+0x10/0x10\n[ 7.350106] ? _raw_spin_lock+0x75/0xe0\n[ 7.350108] kasan_report+0xce/0x100\n[ 7.350109] ? _raw_spin_lock+0x75/0xe0\n[ 7.350114] kasan_check_range+0x105/0x1b0\n[ 7.350116] _raw_spin_lock+0x75/0xe0\n[ 7.350118] ? __pfx__raw_spin_lock+0x10/0x10\n[ 7.350119] ? __call_rcu_common.constprop.0+0x25e/0x780\n[ 7.350125] ? close_id_del_oplock+0x2cc/0x4e0\n[ 7.350128] __ksmbd_close_fd+0x27f/0xaf0\n[ 7.350131] ksmbd_close_fd+0x135/0x1b0\n[ 7.350133] smb2_close+0xb19/0x15b0\n[ 7.350142] ? __pfx_smb2_close+0x10/0x10\n[ 7.350143] ? xas_load+0x18/0x270\n[ 7.350146] ? _raw_spin_lock+0x84/0xe0\n[ 7.350148] ? __pfx__raw_spin_lock+0x10/0x10\n[ 7.350150] ? _raw_spin_unlock+0xe/0x30\n[ 7.350151] ? ksmbd_smb2_check_message+0xeb2/0x24c0\n[ 7.350153] ? ksmbd_tree_conn_lookup+0xcd/0xf0\n[ 7.350154] handle_ksmbd_work+0x40f/0x1080\n[ 7.350156] process_one_work+0x5fa/0xef0\n[ 7.350162] ? assign_work+0x122/0x3e0\n[ 7.350163] worker_thread+0x54b/0xf70\n[ 7.350165] ? __pfx_worker_thread+0x10/0x10\n[ 7.350166] kthread+0x346/0x470\n[ 7.350170] ? recalc_sigpending+0x19b/0x230\n[ 7.350176] ? __pfx_kthread+0x10/0x10\n[ 7.350178] ret_from_fork+0x4fb/0x6c0\n[ 7.350183] ? __pfx_ret_from_fork+0x10/0x10\n[ 7.350185] ? __switch_to+0x36c/0xbe0\n[ 7.350188] ? __pfx_kthread+0x10/0x10\n[ 7.350190] ret_from_fork_asm+0x1a/0x30\n[ 7.350197] </TASK>\n[ 7.350197]\n[ 7.355160] Allocated by task 123:\n[ 7.355261] kasan_save_stack+0x33/0x60\n[ 7.355373] kasan_save_track+0x14/0x30\n[ 7.355484] __kasan_kmalloc+0x8f/0xa0\n[ 7.355593] ksmbd_conn_alloc+0x44/0x6d0\n[ 7.355711] ksmbd_kthread_fn+0x243/0xd70\n[ 7.355839] kthread+0x346/0x470\n[ 7.355942] ret_from_fork+0x4fb/0x6c0\n[ 7.356051] ret_from_fork_asm+0x1a/0x30\n[ 7.356164]\n[ 7.356214] Freed by task 134:\n[ 7.356305] kasan_save_stack+0x33/0x60\n[ 7.356416] kasan_save_track+0x14/0x30\n[ 7.356527] kasan_save_free_info+0x3b/0x60\n[ 7.356646] __kasan_slab_free+0x43/0x70\n[ 7.356761] kfree+0x1ca/0x430\n[ 7.356862] ksmbd_tcp_disconnect+0x59/0xe0\n[ 7.356993] ksmbd_conn_handler_loop+0x77e/0xd40\n[ 7.357138] kthread+0x346/0x470\n[ 7.357240] ret_from_fork+0x4fb/0x6c0\n[ 7.357350] ret_from_fork_asm+0x1a/0x30\n[ 7.357463]\n[ 7.357513] The buggy address belongs to the object at ffff8881056ac000\n[ 7.357513] which belongs to the cache kmalloc-1k of size 1024\n[ 7.357857] The buggy address is located 396 bytes inside of\n[ 7.357857] freed 1024-byte region \n---truncated---"}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.9}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/ ... (truncated)