# CVE-2026-74489: wifi: mac80211: fix tid_tx use-after-free on BA session stop

> A use-after-free in the Linux kernel Wi-Fi subsystem allows attackers to cause denial of service or potentially execute code during Block Ack session teardown.

- **Severity:** High 8.8 (`CVSS:3.1/AV:A/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-74489, GHSA-qpmf-fc23-r543, UBUNTU-CVE-2026-74489

## What is CVE-2026-74489?

CVE-2026-74489 is a high-severity use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

wifi: mac80211: fix tid_tx use-after-free on BA session stop

ieee80211_stop_tx_ba_cb() hands tid_tx to kfree_rcu() through
ieee80211_remove_tid_tx(), and then reads tid_tx->ndp after dropping
sta->lock:

	ieee80211_remove_tid_tx(sta, tid);	/* kfree_rcu(tid_tx, rcu_head) */
	...
	spin_unlock_bh(&sta->lock);

	if (start_txq)
		ieee80211_agg_start_txq(sta, tid, false);

	if (send_delba)
		ieee80211_send_delba(..., tid_tx->ndp);

That read is not covered by an RCU read-side critical section, and it runs
in preemptible process context: both callers hold the wiphy mutex, reaching
it either from the ieee80211_ba_session_work() wiphy work or from
ieee80211_sta_tear_down_BA_sessions() during station teardown.
Softirqs can run in that window too, both from the local_bh_enable() that
ends ieee80211_agg_start_txq() and from any interrupt exit, so the RCU
callback can free tid_tx before the read.

Driving the function from a test module with the grace period forced into
that window, KASAN reports the read, and the free arrives on the ordinary
RCU softirq path:

  BUG: KASAN: slab-use-after-free in ieee80211_stop_tx_ba_cb+0x3cd/0x400
  Read of size 1 at addr ffff888002b9f52e by task kworker/0:1/10
  [...]
  Freed by task 57:
   __kasan_slab_free+0x47/0x70
   __rcu_free_sheaf_prepare+0x70/0x250
   rcu_free_sheaf_nobarn+0x18/0x40
   rcu_core+0x426/0x1310
   handle_softirqs+0x144/0x590
   __irq_exit_rcu+0xea/0x150
   irq_exit_rcu+0x9/0x20
   sysvec_apic_timer_interrupt+0x6b/0x80
   asm_sysvec_apic_timer_interrupt+0x1a/0x20

send_delba is only set when tx_stop is set, which happens for
AGG_STOP_LOCAL_REQUEST alone, so this is reached on local teardown -
session idle timeout, PTK rekey, suspend, HW reconfig - and not from a
peer's DELBA.

Read ndp into a local before the session is freed, while sta->lock is still
held. tid_tx->ndp has a single writer, in
ieee80211_tx_ba_session_handle_start(), which cannot run concurrently here:
both paths are serialised by the wiphy mutex, and the session is already
marked HT_AGG_STATE_STOPPING at this point. tid_tx->ndp is also the only
tid_tx dereference left after ieee80211_remove_tid_tx() in this function.

[move/change the comment a bit to be more general not just on ndp,
 initialize ndp directly]

## Which versions are affected by CVE-2026-74489?


## How do I fix CVE-2026-74489?

Apply the vendor's patch.

## Is CVE-2026-74489 being exploited?

There is no known exploitation of CVE-2026-74489 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74489 and fix it if it is affected.

What it is: CVE-2026-74489 is a high-severity use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74489 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-2026-74489/ (Markdown: https://insights.sbomify.com/CVE-2026-74489/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74489
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74489
- OSV: https://osv.dev/vulnerability/CVE-2026-74489

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74489/
Summaries are generated and may contain mistakes; the official description above is the record.