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CVE-2026-53383— ksmbd: reject non-VALID session in compound request branch

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会开源的一款操作系统内核。 Linux kernel存在安全漏洞，该漏洞源于ksmbd的smb2_check_user_session函数在复合请求分支中未检查会话状态是否为VALID，可能导致远程空指针取消引用和内核崩溃。

CVSS 7.5 · High EPSS 0.66% · P49

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 22

VendorProduct Version RangeStatus
Linux Linux eb947403518ea3d93f6d89264bb1f5416bb0c7d0< 25ff12b82a376ff5c4583102a63d2456a6b9ebb9 affected
854156d12caa9d36de1cf5f084591c7686cc8a9d< fc578523a72cb8b329d32070b95898e81613cc3f affected
5005bcb4219156f1bf7587b185080ec1da08518e< d2bbbb6c55812220fee5d801c275cc267ea3cbeb affected
5005bcb4219156f1bf7587b185080ec1da08518e< 8f0302fb691537d33ec8f668565257ea9d340ffe affected
5005bcb4219156f1bf7587b185080ec1da08518e< 7cad3ceaf679c55bc9946685dacafce78ce6b51a affected
5005bcb4219156f1bf7587b185080ec1da08518e< 06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7 affected
5005bcb4219156f1bf7587b185080ec1da08518e< 5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4 affected
5005bcb4219156f1bf7587b185080ec1da08518e< 609ca17d869d04ba249e32cdcbf13c0b1c66f43c affected
… +14 more rows
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I. Basic Information for CVE-2026-53383

Vulnerability Information
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Vulnerability Title
ksmbd: reject non-VALID session in compound request branch
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: ksmbd: reject non-VALID session in compound request branch smb2_check_user_session() takes a shortcut for any operation that is not the first in a COMPOUND request: it reuses work->sess (the session bound by the first operation) and validates only the SessionId, then returns "valid". It never re-checks work->sess->state == SMB2_SESSION_VALID, and a SessionId of 0xFFFFFFFFFFFFFFFF (ULLONG_MAX, the MS-SMB2 related-operation value) skips even the id comparison. The standalone path (ksmbd_session_lookup_all() plus the SESSION_SETUP state machine) does enforce the VALID state; the compound branch bypasses all of it. A SESSION_SETUP carrying only an NTLM Type-1 (NtLmNegotiate) blob publishes a fresh SMB2_SESSION_IN_PROGRESS session whose sess->user is still NULL (->user is assigned later, by ntlm_authenticate()). Used as operation 1 of a COMPOUND with operation 2 = TREE_CONNECT (related, SessionId=ULLONG_MAX, \\host\IPC$), the tree-connect then runs on that IN_PROGRESS session and reaches ksmbd_ipc_tree_connect_request(), which dereferences user_name(sess->user) with sess->user == NULL (transport_ipc.c:687/701/704) -> remote NULL-pointer dereference and a kernel Oops that wedges the ksmbd worker for all clients. Reject any non-first compound operation that lands on a session which is not SMB2_SESSION_VALID, mirroring the validity the standalone lookup path enforces. SESSION_SETUP itself legitimately runs on an IN_PROGRESS session, but it is never carried as a non-first compound operation, so multi-leg authentication is unaffected by this check.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会开源的一款操作系统内核。 Linux kernel存在安全漏洞，该漏洞源于ksmbd的smb2_check_user_session函数在复合请求分支中未检查会话状态是否为VALID，可能导致远程空指针取消引用和内核崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux eb947403518ea3d93f6d89264bb1f5416bb0c7d0 ~ 25ff12b82a376ff5c4583102a63d2456a6b9ebb9 -
Linux Linux 6.4 -

II. Public POCs for CVE-2026-53383

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III. Intelligence Information for CVE-2026-53383

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Patches & Fixes for CVE-2026-53383 (8)

Same Patch Batch · Linux · 2026-07-19 · 429 CVEs total

CVE-2026-63795 10.0 CRITICAL 9p: avoid putting oldfid in p9_client_walk() error path
CVE-2026-64091 9.8 CRITICAL batman-adv: tt: fix TOCTOU race for reported vlans
CVE-2026-63984 9.8 CRITICAL ipv6: rpl: fix hdrlen overflow in ipv6_rpl_srh_decompress()
CVE-2026-64025 9.8 CRITICAL bpf, skmsg: fix verdict sk_data_ready racing with ktls rx
CVE-2026-63922 9.8 CRITICAL ipv6: exthdrs: refresh nh after handling HAO option
CVE-2026-63979 9.8 CRITICAL net/handshake: hand off the pinned file reference to accept_doit
CVE-2026-64056 9.8 CRITICAL net: ethernet: cortina: Make RX SKB per-port
CVE-2026-63800 9.8 CRITICAL pNFS: Fix use-after-free in pnfs_update_layout()
CVE-2026-63978 9.8 CRITICAL net/handshake: Drain pending requests at net namespace exit
CVE-2026-64055 9.8 CRITICAL net: ethernet: cortina: Carry over frag counter
CVE-2026-63808 9.8 CRITICAL exfat: fix potential use-after-free in exfat_find_dir_entry()
CVE-2026-64033 9.8 CRITICAL RDMA/rtrs: Fix use-after-free in path file creation cleanup
CVE-2026-63888 9.8 CRITICAL scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()
CVE-2026-63887 9.8 CRITICAL scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf
CVE-2026-64113 9.8 CRITICAL ixgbevf: fix use-after-free in VEPA multicast source pruning
CVE-2026-63825 9.8 CRITICAL gcov: use atomic counter updates to fix concurrent access crashes
CVE-2026-63857 9.8 CRITICAL net: airoha: Do not read uninitialized fragment address in airoha_dev_xmit()
CVE-2026-64160 9.8 CRITICAL netfs: Fix potential for tearing in ->remote_i_size and ->zero_point
CVE-2026-64125 9.8 CRITICAL net: bcmgenet: keep RBUF EEE/PM disabled
CVE-2026-63924 9.8 CRITICAL ipv6: exthdrs: refresh nh pointer after ipv6_hop_jumbo()

Showing top 20 of 429 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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