# CVE-2026-31718: ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger

CVE-2026-31718 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-31718, released May 15, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-31718
- Priority: Urgent
- CVSS: 9.8 (Critical)
- EPSS: 0.0036
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 1, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-31718

## Description

In the Linux kernel, the following vulnerability has been resolved:  ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger  When a durable file handle survives session disconnect (TCP close without SMB2_LOGOFF), session_fd_check() sets fp->conn = NULL to preserve the handle for later reconnection. However, it did not clean up the byte-range locks on fp->lock_list.  Later, when the durable scavenger thread times out and calls __ksmbd_close_fd(NULL, fp), the lock cleanup loop did:      spin_lock(&fp->conn->llist_lock);  This caused a slab use-after-free because fp->conn was NULL and the original connection object had already been freed by ksmbd_tcp_disconnect().  The root cause is asymmetric cleanup: lock entries (smb_lock->clist) were left dangling on the freed conn->lock_list while fp->conn was nulled out.  To fix this issue properly, we need to handle the lifetime of smb_lock->clist across three paths:  - Safely skip clist deletion when list is empty and fp->conn is NULL.  - Remove the lock from the old connection's lock_list in    session_fd_check()  - Re-add the lock to the new connection's lock_list in    ksmbd_reopen_durable_fd().

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.85-1 | [DEBIAN-CVE-2026-31718](https://patchblox.com/security/data/fix/linux/debian-cve-2026-31718.md) | May 15, 2026 |
| Linux | linux Debian 14 | 7.0.3-1 | [DEBIAN-CVE-2026-31718](https://patchblox.com/security/data/fix/linux/debian-cve-2026-31718.md) | May 15, 2026 |

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Data as of 2026-11-09T01:18:40Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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