Unity Linux 20.1050a Security Update: kernel (UTSA-2026-100720)

high Nessus Plugin ID 336639

Synopsis

The Unity Linux host is missing one or more security updates.

Description

The Unity Linux 20 host has a package installed that is affected by a vulnerability as referenced in the UTSA-2026-100720 advisory.

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 [email protected]:
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]

Tenable has extracted the preceding description block directly from the Unity Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Update the affected kernel package.

Plugin Details

Severity: High

ID: 336639

File Name: unity_linux_UTSA-2026-100720.nasl

Version: 1.1

Type: Local

Family: Unity Linux Local Security Checks

Published: 8/17/2026

Updated: 8/17/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.9

Percentile: 58.09

CVSS v2

Risk Factor: Medium

Base Score: 6.8

Temporal Score: 5

Vector: CVSS2#AV:L/AC:L/Au:S/C:C/I:C/A:C

CVSS Score Source: CVE-2026-46319

CVSS v3

Risk Factor: High

Base Score: 7.8

Temporal Score: 6.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

Required KB Items: Host/local_checks_enabled, Host/cpu, Host/UOS-Server/release, Host/UOS-Server/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 8/13/2026

Vulnerability Publication Date: 6/9/2026

Reference Information

CVE: CVE-2026-46319

Detections

Analytics