CVE-2026-46319 - Vulnerability Details

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

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]

Published: 2026-06-09

Score: 7.0 High

EPSS: n/a

KEV: No

Impact:

Action:

Analysis

Impact

In the Linux kernel, the act_ct classifier uses a flow table that is looked up via an RCU‑protected rhashtable. The code releases the RCU lock before incrementing the reference count. A race exists in which the table entry can be freed by cleanup work queued through call_rcu, so that the reference count is still incremented after the object has been freed. This causes a use‑after‑free that allows an attacker to execute arbitrary code in kernel mode. The flaw is a classic Use‑After‑Free (CWE‑416) and can lead to privilege escalation.

Affected Systems

The vulnerability affects any Linux kernel that has act_ct enabled, which is common on systems that use the ‘tc’ traffic control classifier to match on connection‑tracking state. All distributions shipping a kernel with the net/sched act_ct implementation are potentially vulnerable until the upstream fix is backported. Devices such as routers or virtual machines that load the act_ct module for QoS or traffic shaping are also at risk.

Risk and Exploitability

No publicly known exploit and the race window is very small, making manual exploitation difficult; no EPSS score is available. The CVSS score is 7.0, indicating a high severity because kernel privilege escalation is possible. The issue is not in the CISA KEV catalog yet. Until a vendor releases a patch, the risk remains significant, but triggering the flaw requires privileged access or elevated capabilities to create the race scenario.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`138470a9b2cc2e26e6018300394afc3858a54e6a`	affected	< ece578ca61e572df96cfc80456357ebfae0b4b9e
`138470a9b2cc2e26e6018300394afc3858a54e6a`	affected	< a2e0c045c87aa252eb61412e67dd91f2c2b19f81
`138470a9b2cc2e26e6018300394afc3858a54e6a`	affected	< 67c9ecc9f2575273ed1323e312881fc98ac83d6d
`138470a9b2cc2e26e6018300394afc3858a54e6a`	affected	< f23424a0ddadb494d4bd57056a7ca703312d3a7b
`138470a9b2cc2e26e6018300394afc3858a54e6a`	affected	< 17dfb67cb399b660105d9a8c6100851c0d0cdc70
`138470a9b2cc2e26e6018300394afc3858a54e6a`	affected	< 4c727c6967a41b37efe0f26332ca9ec5b74785a3
`138470a9b2cc2e26e6018300394afc3858a54e6a`	affected	< 3e20e1b3058e0b94638e7b931c138e840e266724
`138470a9b2cc2e26e6018300394afc3858a54e6a`	affected	< f462dca0c8415bf0058d0ffa476354c4476d0f09

Linux

affected

Version	Status	Constraints
`5.7`	affected	—
`0`	unaffected	< 5.7
`5.10.258`	unaffected	≤ 5.10.*
`5.15.209`	unaffected	≤ 5.15.*
`6.1.175`	unaffected	≤ 6.1.*
`6.6.141`	unaffected	≤ 6.6.*
`6.12.91`	unaffected	≤ 6.12.*
`6.18.33`	unaffected	≤ 6.18.*
`7.0.10`	unaffected	≤ 7.0.*
`7.1-rc1`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[138470a9b2cc2e26e6018300394afc3858a54e6a,ece578ca61e572df96cfc80456357ebfae0b4b9e)`	affected	code_commit	—
`[138470a9b2cc2e26e6018300394afc3858a54e6a,a2e0c045c87aa252eb61412e67dd91f2c2b19f81)`	affected	code_commit	—
`[138470a9b2cc2e26e6018300394afc3858a54e6a,67c9ecc9f2575273ed1323e312881fc98ac83d6d)`	affected	code_commit	—
`[138470a9b2cc2e26e6018300394afc3858a54e6a,f23424a0ddadb494d4bd57056a7ca703312d3a7b)`	affected	code_commit	—
`[138470a9b2cc2e26e6018300394afc3858a54e6a,17dfb67cb399b660105d9a8c6100851c0d0cdc70)`	affected	code_commit	—
`[138470a9b2cc2e26e6018300394afc3858a54e6a,4c727c6967a41b37efe0f26332ca9ec5b74785a3)`	affected	code_commit	—
`[138470a9b2cc2e26e6018300394afc3858a54e6a,3e20e1b3058e0b94638e7b931c138e840e266724)`	affected	code_commit	—
`[138470a9b2cc2e26e6018300394afc3858a54e6a,f462dca0c8415bf0058d0ffa476354c4476d0f09)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`5.7`	affected	generic	—
`[0,5.7)`	unaffected	generic	—
`[5.10.258,6.0.0)`	unaffected	semver	—
`[5.15.209,6.0.0)`	unaffected	semver	—
`[6.1.175,7.0.0)`	unaffected	semver	—
`[6.6.141,7.0.0)`	unaffected	semver	—
`[6.12.91,7.0.0)`	unaffected	semver	—
`[6.18.33,7.0.0)`	unaffected	semver	—
`[7.0.10,8.0.0)`	unaffected	semver	—
`[7.1-rc1,*]`	unaffected	generic	—

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Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

Apply the latest Linux kernel release that contains the act_ct race condition fix.
If an immediate kernel upgrade is not possible, disable act_ct functionality by unloading the module or removing the tc act_ct classifier from the network configuration.
Configure audit or monitoring to flag any unexpected rcu work or ct_ft frees that might indicate an ongoing attempt to exploit the race window.

Generated by OpenCVE AI on June 10, 2026 at 02:12 UTC.

Tracking

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Advisories

No advisories yet.

No CVSS v4.0

Attack Vector Local

Attack Complexity High

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/17dfb67cb399b660105d9a8c6100851c0d0cdc70
https://git.kernel.org/stable/c/3e20e1b3058e0b94638e7b931c138e840e266724
https://git.kernel.org/stable/c/4c727c6967a41b37efe0f26332ca9ec5b74785a3
https://git.kernel.org/stable/c/67c9ecc9f2575273ed1323e312881fc98ac83d6d
https://git.kernel.org/stable/c/a2e0c045c87aa252eb61412e67dd91f2c2b19f81
https://git.kernel.org/stable/c/ece578ca61e572df96cfc80456357ebfae0b4b9e
https://git.kernel.org/stable/c/f23424a0ddadb494d4bd57056a7ca703312d3a7b
https://git.kernel.org/stable/c/f462dca0c8415bf0058d0ffa476354c4476d0f09
https://lore.kernel.org/linux-cve-announce/2026060925-CVE-2026-46319-ab3d@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2026-46319
https://www.cve.org/CVERecord?id=CVE-2026-46319

History

Wed, 10 Jun 2026 02:30:00 +0000

Type	Values Removed	Values Added
Weaknesses	CWE-416

Wed, 10 Jun 2026 00:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-826
References		https://lore.kernel.org/linux-cve-announce/2026060925-CVE-2026-46319-ab3d@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2026-46319 https://www.cve.org/CVERecord?id=CVE-2026-46319
Metrics	threat_severity `None`	cvssV3_1 `{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}` threat_severity `Important`

Tue, 09 Jun 2026 13:45:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-416

Tue, 09 Jun 2026 12:30:00 +0000

Type	Values Removed	Values Added
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]
Title		net/sched: act_ct: Only release RCU read lock after ct_ft
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/17dfb67cb399b660105d9a8c6100851c0d0cdc70 https://git.kernel.org/stable/c/3e20e1b3058e0b94638e7b931c138e840e266724 https://git.kernel.org/stable/c/4c727c6967a41b37efe0f26332ca9ec5b74785a3 https://git.kernel.org/stable/c/67c9ecc9f2575273ed1323e312881fc98ac83d6d https://git.kernel.org/stable/c/a2e0c045c87aa252eb61412e67dd91f2c2b19f81 https://git.kernel.org/stable/c/ece578ca61e572df96cfc80456357ebfae0b4b9e https://git.kernel.org/stable/c/f23424a0ddadb494d4bd57056a7ca703312d3a7b https://git.kernel.org/stable/c/f462dca0c8415bf0058d0ffa476354c4476d0f09

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-06-09T12:11:12.128Z

Updated: 2026-06-09T12:11:12.128Z

Reserved: 2026-05-13T15:03:33.112Z

Link: CVE-2026-46319

Vulnrichment

No data.

NVD

Status : Received

Published: 2026-06-09T13:16:37.210

Modified: 2026-06-09T13:16:37.210

Link: CVE-2026-46319

Redhat

Severity : Important

Publid Date: 2026-06-09T00:00:00Z

Links: CVE-2026-46319 - Bugzilla

OpenCVE Enrichment

Updated: 2026-06-10T02:15:19Z

Weaknesses

CWE-826

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Local

Attack Complexity High

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

Subscriptions

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