# CVE-2026-89635: ksmbd: only rebind the reopened file's own oplock on durable reconnect

> An authenticated attacker can trigger a use-after-free in the Linux kernel's ksmbd module by reconnecting durable handles, potentially leading to code execution or system crash.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** GHSA-rg7m-2q29-w52v, UBUNTU-CVE-2026-89635

## What is CVE-2026-89635?

CVE-2026-89635 is a critical use after free vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ksmbd: only rebind the reopened file's own oplock on durable reconnect

ksmbd_reopen_durable_fd() walks the inode's m_op_list and rebinds every
detached oplock to the reconnecting session:

	list_for_each_entry_rcu(op, &ci->m_op_list, op_entry,
				lockdep_is_held(&ci->m_lock)) {
		if (op->conn)
			continue;
		op->conn = ksmbd_conn_get(fp->conn);
		op->sess = work->sess;
	}

The only key is op->conn == NULL, which every detached durable handle on
that inode matches, not just the one owned by fp.  When two sessions hold
durable handles on the same file and both disconnect, reconnecting one of
them adopts the other session's oplock: op->sess is overwritten with the
reconnecting session without taking a reference on it, while op->conn
pins the connection.

The sibling teardown path, session_fd_check(), keys on the identity of
the connection being torn down (op->conn == conn) rather than on shared
state, and so does not have this problem.

Once the adopting session is destroyed, ksmbd_session_destroy() frees it
while the foreign oplock still points at it.  The reader in
ksmbd_close_fd_app_instance_id() validates only opinfo->conn, which is
still live thanks to the reference taken above, and then dereferences the
stale session:

	if (!opinfo->conn) {
		up_read(&fp->f_ci->m_lock);
		goto out;
	}

	ft = &opinfo->sess->file_table;
	write_lock(&ft->lock);

  BUG: KASAN: slab-use-after-free in _raw_write_lock+0x74/0xd0
  Write of size 4 at addr ffff88810a970528 by task kworker/0:0/9
  Workqueue: ksmbd-io handle_ksmbd_work
  Call Trace:
   _raw_write_lock+0x74/0xd0
   ksmbd_close_fd_app_instance_id+0x183/0x410
   smb2_open+0x1346/0x4430
   handle_ksmbd_work+0x2bb/0x7b0

Reached from an authenticated session against a share with the default
durable-handle and oplock configuration: two sessions open the same file
with a durable-v2 handle and an RH lease under distinct AppInstanceIds,
both log off, one reconnects with DH2C, and a later durable-v2 create
carrying the other AppInstanceId walks into the freed session.

Constrain the loop to the oplock owned by the file being reopened.

## Which versions are affected by CVE-2026-89635?


## How do I fix CVE-2026-89635?

Apply the vendor's patch.

## Is CVE-2026-89635 being exploited?

There is no known exploitation of CVE-2026-89635 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89635 and fix it if it is affected.

What it is: CVE-2026-89635 is a critical use after free vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89635 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89635/ (Markdown: https://insights.sbomify.com/CVE-2026-89635/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89635
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89635
- OSV: https://osv.dev/vulnerability/CVE-2026-89635

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89635/
Summaries are generated and may contain mistakes; the official description above is the record.