Linux Kernel up to 7.2.5/7.3-rc1 ksmbd fs/smb/server/smb2pdu.c smb2_tree_connect use after free

Summaryinfo

A vulnerability was found in Linux Kernel up to 7.2.5/7.3-rc1. It has been classified as very critical. This impacts the function smb2_tree_connect of the file fs/smb/server/smb2pdu.c of the component ksmbd. The manipulation leads to use after free. This vulnerability is uniquely identified as CVE-2026-89788. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.2.5/7.3-rc1. It has been rated as very critical. This issue affects the function smb2_tree_connect of the file fs/smb/server/smb2pdu.c of the component ksmbd. The manipulation with an unknown input leads to a use after free vulnerability. Using CWE to declare the problem leads to CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix tree connection use-after-free in smb2_tree_connect() ksmbd_tree_conn_connect() publishes a new tree connection in sess->tree_conns with a single reference and returns its pointer to smb2_tree_connect(). The handler continues to initialize the object and build the response after publication. A concurrent session logoff can erase the connection and drop that reference, freeing the object while the handler still uses it. BUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90 smb2_tree_connect (fs/smb/server/smb2pdu.c:2872) handle_ksmbd_work process_one_work worker_thread kthread After xa_store() succeeds, take a second reference before releasing tree_conns_lock. The original reference belongs to the xarray entry and the second belongs to the creating smb2_tree_connect() handler. Keep the references balanced in every path: - On normal exit or an error after publication, smb2_tree_connect() drops its creator reference. Error cleanup also calls ksmbd_tree_conn_disconnect(), which drops the xarray reference only if it removes the exact entry. - SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop its xarray reference. The request's existing lookup reference remains owned by the request and is released by the existing cleanup. - Session LOGOFF removes each entry and drops its xarray reference. If it wins the race, later cleanup sees that the entry is gone and does not drop that reference again. To enforce this ownership, claim the disconnected state and erase the exact entry atomically under tree_conns_lock. This guarantees one drop for the xarray reference and one drop by each in-flight user, regardless of which teardown path wins. If logoff removes the entry before initialization completes, fail the connect instead of marking the detached object TREE_CONNECTED.

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2026-89788 since 09/11/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details are known, but no exploit is available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 09/16/2026).

Upgrading to version 7.2.6 or 7.3-rc2 eliminates this vulnerability. Applying the patch 4e30fbd26e84efa2e5cbec4eb11e126ac0c79313/b5ec6c462aab1062cf5d1e667ba7c6442f737055 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-80309). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.3-rc1

License

• open-source

Website

• Vendor: https://www.kernel.org/

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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