VulnerabilityPublished 16 Sep 2026Updated 30 Oct 2026

CVE-2026-89788: Linux kernel · ksmbd: fix tree connection use-after-free in smb2_tree_connect()

Source GCVE Database

Authoritative record:CVE-2026-89788· Critical 9.8

Not known to be exploited · CVSS 9.8 Critical · fixed in ca3a3984bf445aaec69f6937f11e560d4b849365 : patch Linux kernel as a priority.

Data as of 30 Oct 2026, 18:32 UTC

CVSS 3.1 base score

9.8Critical

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (Linux)	CVSS 3.1	9.8

Patch: Available – fixed in ca3a3984bf445aaec69f6937f11e560d4b849365, bd58a52738f7576ee5f5eb74243df13f902c8051, b5ec6c462aab1062cf5d1e667ba7c6442f737055 +4

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

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

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-29wc-2986-775f

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected >=6.1.71 <6.1.191 >=5.15.145 <5.16	Fixed in ca3a3984bf445aaec69f6937f11e560d4b849365 bd58a52738f7576ee5f5eb74243df13f902c8051 b5ec6c462aab1062cf5d1e667ba7c6442f737055 63f5939b50470ef4d245c16d2098376b952beb51 6.1.191 5.16 4e30fbd26e84efa2e5cbec4eb11e126ac0c79313
LinuxLinux	Affected =6.6	Fixed in–

AI-suggested

A fix for this vulnerability has been implemented in the Linux kernel source code. Users and administrators should update to the fixed kernel version once it is released. No alternative mitigations are specified. Since this is not a cloud service, patching the affected Linux kernel is required to remediate the issue.

Description

CVE-2026-89788 is a critical use-after-free vulnerability in the Linux kernel's ksmbd component, specifically in the smb2_tree_connect() function. The flaw arises when a new tree connection is published but concurrently removed due to a session logoff, leading to use of a freed object. This can cause kernel memory corruption and potentially allow an attacker to execute arbitrary code or cause a denial of service.

Impact

This vulnerability allows an attacker to trigger a use-after-free condition in the Linux kernel's SMB server implementation, potentially leading to kernel memory corruption. The CVSS score of 9.8 indicates critical impact with high confidentiality, integrity, and availability consequences. Exploitation could result in arbitrary code execution at kernel level or denial of service.

Summary

The vulnerability in ksmbd involves improper reference counting of tree connection objects in smb2_tree_connect(). After publishing a new tree connection in sess->tree_conns, the handler continues initialization while a concurrent session logoff can remove the connection and free the object. This results in a use-after-free condition detected by KASAN. The fix involves taking a second reference after xa_store() succeeds to ensure the object remains valid during initialization, and carefully balancing reference drops across all code paths including normal exit, error cleanup, SMB2 TREE_DISCONNECT, and session LOGOFF. Atomic operations under tree_conns_lock enforce ownership and prevent double frees or use-after-free scenarios.

References

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