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Linux kernel ksmbd CVE-2026-52911

| EUVDEUVD-2026-38148 HIGH
2026-06-21 Linux GHSA-593m-gq54-r4vq
Information Disclosure Linux Red Hat Suse
8.8
CVSS 3.1 · Vendor: Linux
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Severity by source

Vendor (Linux) PRIMARY
8.8 HIGH
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
5.9 MEDIUM

Authenticated SMB session needed (PR:L) and exploitation depends on the multichannel binding slowpath plus a concurrent victim session (AC:H); impact is primarily unauthorized session read (C:H), limited integrity, no availability.

3.1 AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N
4.0 AV:N/AC:H/AT:N/PR:L/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
SUSE
6.4 MEDIUM
AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H

Primary rating from Vendor (Linux).

CVSS VectorVendor: Linux

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

5
Analysis Generated
Jun 28, 2026 - 10:32 vuln.today
CVSS changed
Jun 28, 2026 - 08:22 NVD
8.8 (HIGH)
Patch available
Jun 21, 2026 - 09:16 EUVD
CVE Published
Jun 21, 2026 - 06:18 cve.org
UNKNOWN (no severity yet)
CVE Published
Jun 21, 2026 - 06:18 cve.org
HIGH 8.8

DescriptionCVE.org

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: scope conn->binding slowpath to bound sessions only

When the binding SESSION_SETUP sets conn->binding = true, the flag stays set after the call so that the global session lookup in ksmbd_session_lookup_all() can find the session, which was not added to conn->sessions. Because the flag is connection-wide, the global lookup path will also resolve any other session by id if asked.

Tighten the global lookup so that the returned session must have this connection registered in its channel xarray (sess->ksmbd_chann_list). The channel entry is installed by the existing binding_session path in ntlm_authenticate()/krb5_authenticate() when a SESSION_SETUP completes successfully, so this condition is a strict equivalent of "this connection has been accepted as a channel of this session". Connections that have not bound to a given session cannot reach it via the global table.

The existing conn->binding gate for entering the slowpath is preserved so that non-binding connections keep the fast-path-only behavior, and the session->state check is unchanged.

AnalysisAI

Improper session authorization in the Linux kernel's in-kernel SMB3 server (ksmbd) lets an authenticated SMB client reach sessions it never bound to. Because the connection-wide conn->binding flag stays set after a binding SESSION_SETUP, the global lookup in ksmbd_session_lookup_all() would resolve any session by ID, allowing a low-privileged remote user to access another user's session (Information Disclosure tagged). No public exploit identified at time of analysis; EPSS is low (0.18%, 7th percentile) and it is not in CISA KEV.

Technical ContextAI

ksmbd is the kernel-space SMB3 file-server introduced in Linux 5.15 as a faster alternative to userspace Samba. SMB3 multichannel allows a session to be 'bound' across multiple TCP connections; during binding, ksmbd sets a connection-wide conn->binding flag and registers the connection in the session's channel xarray (sess->ksmbd_chann_list) via ntlm_authenticate()/krb5_authenticate(). The defect is an improper-authorization class issue (CWE-285/CWE-863, CWE field reported N/A): the global session lookup honored only the connection-wide binding flag, not whether THIS connection was an accepted channel of the target session, so any session could be resolved by ID. The fix tightens the lookup to require the connection to be present in the target session's channel xarray, making access a strict equivalent of 'this connection is an accepted channel of this session.' CPE data identifies the affected component generically as cpe:2.3:a:linux:linux:*.

RemediationAI

Vendor-released patch: upgrade to a fixed kernel - 5.15.209, 6.1.175, 6.6.141, 6.12.91, 7.0.10, 6.18.33, or mainline 7.1 (or later in each series); Debian users should apply DSA-6355-1 (https://security-tracker.debian.org/tracker/dsa-6355-1). The stable commits are available at git.kernel.org (e.g. https://git.kernel.org/stable/c/e74c00c6af428a39e564cdc5bd3a3648c6d8de87). If patching cannot be done immediately, the most effective compensating control is to disable the ksmbd kernel module where it is not needed (rmmod/blacklist ksmbd) since most environments use userspace Samba instead - the trade-off is loss of any in-kernel SMB serving on that host. Where ksmbd must run, restrict access to the SMB service (TCP 445) to trusted clients via firewall rules and limit to authenticated, trusted users, and consider disabling SMB3 multichannel to suppress the binding slowpath, accepting reduced throughput/redundancy as the side effect.

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Vendor StatusVendor

Debian

linux
Release Status Fixed Version Urgency
bullseye not-affected - -
bullseye (security) fixed 5.10.257-1 -
bookworm vulnerable 6.1.170-3 -
bookworm (security) vulnerable 6.1.174-1 -
trixie fixed 6.12.94-1 -
trixie (security) vulnerable 6.12.90-2 -
forky fixed 7.0.12-2 -
sid fixed 7.0.13-1 -
(unstable) fixed 7.0.10-1 -
DSA-6355-1

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Availability Extension 15 SP7 Not-Affected
SUSE Linux Enterprise High Availability Extension 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected

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CVE-2026-52911 vulnerability details – vuln.today
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