CVE-2026-53383

Aliases:UBUNTU-CVE-2026-53383DEBIAN-CVE-2026-53383
Advisory lineage Upstream: 0 Downstream: 9
Analyzed
Published: 19 Jul 2026, 11:59
Last modified:17 Aug 2026, 04:50

Vulnerability Summary

Overall Risk (default)
medium
30/100
CVSS Score
7.5 HIGH
v3.1 (cve.org)
EPSS Score
0.66% LOW
1% probability 0.00%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

19 Jul 2026, 11:59
Published
Vulnerability first disclosed
17 Aug 2026, 04:50
Last Modified
Vulnerability information updated

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.

CVSS Metrics

  • v3.1•HIGH•Score: 7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Trends

Current EPSS score: 0.66%• Percentile: 50%

Techniques & Countermeasures

  • CWE-476•NULL Pointer Dereference

    The product dereferences a pointer that it expects to be valid but is NULL.

Affected Systems

  • debian•linux

    < 6.1.177-1 | < 6.12.95-1 | < 7.0.14-1

  • debian•linux-6.1

    < 6.1.177-1~deb11u1

  • ubuntu•linux

    all | all | all | < 7.0.0-31.31

  • ubuntu•linux-allwinner-5.19

    all

  • ubuntu•linux-aws

    all | all | all | < 7.0.0-1012.12

  • ubuntu•linux-aws-5.0

    all

  • ubuntu•linux-aws-5.11

    all

  • ubuntu•linux-aws-5.13

    all

  • ubuntu•linux-aws-5.15

    all

  • ubuntu•linux-aws-5.19

    all

  • ubuntu•linux-aws-5.3

    all

  • ubuntu•linux-aws-5.8

    all

  • ubuntu•linux-aws-6.14

    all

  • ubuntu•linux-aws-6.17

    all

  • ubuntu•linux-aws-6.2

    all

  • ubuntu•linux-aws-6.5

    all

  • ubuntu•linux-aws-6.8

    all

  • ubuntu•linux-aws-7.0

    all | < 7.0.0-1012.12~24.04.1

  • ubuntu•linux-aws-fips

    all

  • ubuntu•linux-azure

    all | all | all | all

  • ubuntu•linux-azure-5.11

    all

  • ubuntu•linux-azure-5.13

    all

  • ubuntu•linux-azure-5.15

    all

  • ubuntu•linux-azure-5.19

    all

  • ubuntu•linux-azure-5.3

    all

  • ubuntu•linux-azure-5.8

    all

  • ubuntu•linux-azure-6.11

    all

  • ubuntu•linux-azure-6.14

    all

  • ubuntu•linux-azure-6.17

    all

  • ubuntu•linux-azure-6.2

    all

  • ubuntu•linux-azure-6.5

    all

  • ubuntu•linux-azure-6.8

    all

  • ubuntu•linux-azure-7.0

    all

  • ubuntu•linux-azure-edge

    all

  • ubuntu•linux-azure-fde

    all | all | all | all

  • ubuntu•linux-azure-fde-5.15

    all

  • ubuntu•linux-azure-fde-5.19

    all

  • ubuntu•linux-azure-fde-6.14

    all

  • ubuntu•linux-azure-fde-6.17

    all

  • ubuntu•linux-azure-fde-6.2

    all

  • ubuntu•linux-azure-fde-6.8

    all

  • ubuntu•linux-azure-fde-7.0

    all

  • ubuntu•linux-azure-fips

    all

  • ubuntu•linux-azure-nvidia

    all

  • ubuntu•linux-azure-nvidia-6.14

    all

  • ubuntu•linux-bluefield

    all

  • ubuntu•linux-fips

    all

  • ubuntu•linux-gcp

    all | all | all | all | < 7.0.0-1011.11

  • ubuntu•linux-gcp-5.11

    all

  • ubuntu•linux-gcp-5.13

    all

Showing first 50 affected entries in server-rendered view.

References (17)