# CVE-2026-46319: net/sched: act_ct: Only release RCU read lock after ct_ft

> A use-after-free vulnerability in the Linux kernel's net/sched act_ct module allows local attackers to escalate privileges due to improper RCU lock handling.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Jun 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-89681, BELL-CVE-2026-46319, DEBIAN-CVE-2026-46319, GHSA-q9hw-vhj5-hw57, ROOT-OS-DEBIAN-11-CVE-2026-46319, ROOT-OS-DEBIAN-12-CVE-2026-46319, ROOT-OS-DEBIAN-13-CVE-2026-46319, ROOT-OS-UBUNTU-2204-CVE-2026-46319, ROOT-OS-UBUNTU-2404-CVE-2026-46319, UBUNTU-CVE-2026-46319

## What is CVE-2026-46319?

CVE-2026-46319 is a high-severity use after free vulnerability in Linux kernel, published on 9 Jun 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:

net/sched: act_ct: Only release RCU read lock after ct_ft

When looking up a flow table in act_ct in tcf_ct_flow_table_get(),
rhashtable_lookup_fast() internally opens and closes an RCU read critical
section before returning ct_ft.
The tcf_ct_flow_table_cleanup_work() can complete before refcount_inc_not_zero()
is invoked on the returned ct_ft resulting in a UAF on the already freed ct_ft
object. This vulnerability can lead to privilege escalation.

Analysis from zdi-disclosures@trendmicro.com:
When initializing act_ct, tcf_ct_init() is called, which internally triggers
tcf_ct_flow_table_get().

static int tcf_ct_flow_table_get(struct net *net, struct tcf_ct_params *params)

{
                struct zones_ht_key key = { .net = net, .zone = params->zone };
                struct tcf_ct_flow_table *ct_ft;
                int err = -ENOMEM;

                mutex_lock(&zones_mutex);
                ct_ft = rhashtable_lookup_fast(&zones_ht, &key, zones_params); // [1]
                if (ct_ft && refcount_inc_not_zero(&ct_ft->ref)) // [2]
                                goto out_unlock;
                ...
}

static __always_inline void *rhashtable_lookup_fast(
                struct rhashtable *ht, const void *key,
                const struct rhashtable_params params)
{
                void *obj;

                rcu_read_lock();
                obj = rhashtable_lookup(ht, key, params);
                rcu_read_unlock();

                return obj;
}

At [1], rhashtable_lookup_fast() looks up and returns the corresponding ct_ft
from zones_ht . The lookup is performed within an RCU read critical section
through rcu_read_lock() / rcu_read_unlock(), which prevents the object from
being freed. However, at the point of function return, rcu_read_unlock() has
already been called, and there is nothing preventing ct_ft from being freed
before reaching refcount_inc_not_zero(&ct_ft->ref) at [2]. This interval becomes
the race window, during which ct_ft can be freed.

Free Process:

tcf_ct_flow_table_put() is executed through the path tcf_ct_cleanup() call_rcu()
tcf_ct_params_free_rcu() tcf_ct_params_free() tcf_ct_flow_table_put().

static void tcf_ct_flow_table_put(struct tcf_ct_flow_table *ct_ft)
{
                if (refcount_dec_and_test(&ct_ft->ref)) {
                                rhashtable_remove_fast(&zones_ht, &ct_ft->node, zones_params);
                                INIT_RCU_WORK(&ct_ft->rwork, tcf_ct_flow_table_cleanup_work); // [3]
                                queue_rcu_work(act_ct_wq, &ct_ft->rwork);
                }
}

At [3], tcf_ct_flow_table_cleanup_work() is scheduled as RCU work

static void tcf_ct_flow_table_cleanup_work(struct work_struct *work)

{
                struct tcf_ct_flow_table *ct_ft;
                struct flow_block *block;

                ct_ft = container_of(to_rcu_work(work), struct tcf_ct_flow_table,
                                                                rwork);
                nf_flow_table_free(&ct_ft->nf_ft);
                block = &ct_ft->nf_ft.flow_block;
                down_write(&ct_ft->nf_ft.flow_block_lock);
                WARN_ON(!list_empty(&block->cb_list));
                up_write(&ct_ft->nf_ft.flow_block_lock);
                kfree(ct_ft); // [4]

                module_put(THIS_MODULE);
}

tcf_ct_flow_table_cleanup_work() frees ct_ft at [4]. When this function executes
between [1] and [2], UAF occurs.

This race condition has a very short race window, making it generally
difficult to trigger. Therefore, to trigger the vulnerability an msleep(100) was
inserted after[1]

Weakness: CWE-416 (Use After Free), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-46319?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-46319?

Apply the vendor's patch.

## Is CVE-2026-46319 being exploited?

There is no known exploitation of CVE-2026-46319 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-46319 and fix it if it is affected.

What it is: CVE-2026-46319 is a high-severity use after free vulnerability in Linux kernel, published on 9 Jun 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-2026-46319 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-46319/ (Markdown: https://insights.sbomify.com/CVE-2026-46319/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-46319
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-46319
- OSV: https://osv.dev/vulnerability/CVE-2026-46319

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-46319/
Summaries are generated and may contain mistakes; the official description above is the record.