# CVE-2026-98173: smb: client: fix use-after-free of iface in cifs_try_adding_channels()

> A use-after-free in the Linux kernel SMB client allows attackers to cause denial of service or execute arbitrary code via concurrent interface refreshes.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-106143, BELL-CVE-2026-98173, DEBIAN-CVE-2026-98173, GHSA-7vf5-5xh7-53fm, UBUNTU-CVE-2026-98173

## What is CVE-2026-98173?

CVE-2026-98173 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

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

smb: client: fix use-after-free of iface in cifs_try_adding_channels()

cifs_try_adding_channels() iterates ses->iface_list with
list_for_each_entry_safe_from(), which captures the next entry
(niface) under iface_lock.  The loop body then drops iface_lock for
the whole duration of cifs_ses_add_channel().

A concurrent interface refresh (SMB3_request_interfaces() ->
parse_server_interfaces()) marks all ifaces inactive and removes and
frees any that are not re-advertised via list_del() + kref_put(),
where release_iface() is a bare kfree().  Since niface typically has
no channel holding a reference, the list reference is its last and it
can be freed inside the unlocked window.  On continue, the iterator
advance step then dereferences niface->iface_head.next, and the loop
body reads iface->rdma_capable/is_active, both on freed memory.

Fix this by never keeping an unreferenced list pointer across the
unlocked window.  Each channel attempt now re-scans the list from the
head under iface_lock, takes a kref on the selected candidate, and
passes only that referenced candidate to cifs_ses_add_channel().
weight_fulfilled still tracks selection progress, so restarting the
scan preserves the original weighted distribution and the
weight_fulfilled-before-kref_put ordering on the failure path.

Add a per-pass attempts cap so a flapping interface refresh cannot
keep the inner loop spinning within a single tries increment.

## Which versions are affected by CVE-2026-98173?


## How do I fix CVE-2026-98173?

Apply the vendor's patch.

## Is CVE-2026-98173 being exploited?

There is no known exploitation of CVE-2026-98173 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98173 and fix it if it is affected.

What it is: CVE-2026-98173 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-98173 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-2026-98173/ (Markdown: https://insights.sbomify.com/CVE-2026-98173/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98173
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98173
- OSV: https://osv.dev/vulnerability/CVE-2026-98173

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98173/
Summaries are generated and may contain mistakes; the official description above is the record.