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

CVE-2026-89788 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-89788, released September 23, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-89788
- Priority: Urgent
- CVSS: 9.8 (Critical)
- EPSS: 0.0064
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 16, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-89788

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-89788](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89788.md) | Sep 23, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-89788](https://patchblox.com/security/data/fix/linux/debian-cve-2026-89788.md) | Sep 23, 2026 |

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Data as of 2026-11-09T13:31:49Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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