Linux Kernel up to 6.16.5 br_netfilter_hooks.c br_nf_local_in hash privilege escalation

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4.9	$0-$5k	0.00

Summaryinfo

A vulnerability labeled as critical has been found in Linux Kernel up to 5.15.191/6.1.150/6.6.104/6.12.45/6.16.5. The impacted element is the function br_nf_local_in of the file net/bridge/br_netfilter_hooks.c. Executing a manipulation of the argument hash can lead to an unknown weakness. This vulnerability is handled as CVE-2025-39894. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as critical was found in Linux Kernel up to 5.15.191/6.1.150/6.6.104/6.12.45/6.16.5. This vulnerability affects the function br_nf_local_in of the file net/bridge/br_netfilter_hooks.c. The manipulation of the argument hash with an unknown input leads to a unknown weakness. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: netfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after confirm When send a broadcast packet to a tap device, which was added to a bridge, br_nf_local_in() is called to confirm the conntrack. If another conntrack with the same hash value is added to the hash table, which can be triggered by a normal packet to a non-bridge device, the below warning may happen. ------------[ cut here ]------------ WARNING: CPU: 1 PID: 96 at net/bridge/br_netfilter_hooks.c:632 br_nf_local_in+0x168/0x200 CPU: 1 UID: 0 PID: 96 Comm: tap_send Not tainted 6.17.0-rc2-dirty #44 PREEMPT(voluntary) RIP: 0010:br_nf_local_in+0x168/0x200 Call Trace: <TASK> nf_hook_slow+0x3e/0xf0 br_pass_frame_up+0x103/0x180 br_handle_frame_finish+0x2de/0x5b0 br_nf_hook_thresh+0xc0/0x120 br_nf_pre_routing_finish+0x168/0x3a0 br_nf_pre_routing+0x237/0x5e0 br_handle_frame+0x1ec/0x3c0 __netif_receive_skb_core+0x225/0x1210 __netif_receive_skb_one_core+0x37/0xa0 netif_receive_skb+0x36/0x160 tun_get_user+0xa54/0x10c0 tun_chr_write_iter+0x65/0xb0 vfs_write+0x305/0x410 ksys_write+0x60/0xd0 do_syscall_64+0xa4/0x260 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> ---[ end trace 0000000000000000 ]--- To solve the hash conflict, nf_ct_resolve_clash() try to merge the conntracks, and update skb->_nfct. However, br_nf_local_in() still use the old ct from local variable 'nfct' after confirm(), which leads to this warning. If confirm() does not insert the conntrack entry and return NF_DROP, the warning may also occur. There is no need to reserve the WARN_ON_ONCE, just remove it.

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2025-39894 since 04/16/2025. The exploitation appears to be difficult. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 269669 (Linux Distros Unpatched Vulnerability : CVE-2025-39894), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.15.192, 6.1.151, 6.6.105, 6.12.46 or 6.16.6 eliminates this vulnerability. Applying the patch d00c8b0daf56012f69075e3377da67878c775e4c/ccbad4803225eafe0175d3cb19f0d8d73b504a94/50db11e2bbb635e38e3dd096215580d6adb41fb0/c47ca77fee9071aa543bae592dd2a384f895c8b6/a74abcf0f09f59daeecf7a3ba9c1d690808b0afe/479a54ab92087318514c82428a87af2d7af1a576 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (269669) and CERT Bund (WID-SEC-2025-2170). Once again VulDB remains the best source for vulnerability data.

Affected

• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Linux Kernel
• Dell Secure Connect Gateway

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 5.15.191
• 6.1.150
• 6.6.104
• 6.12.0
• 6.12.1
• 6.12.2
• 6.12.3
• 6.12.4
• 6.12.5
• 6.12.6
• 6.12.7
• 6.12.8
• 6.12.9
• 6.12.10
• 6.12.11
• 6.12.12
• 6.12.13
• 6.12.14
• 6.12.15
• 6.12.16
• 6.12.17
• 6.12.18
• 6.12.19
• 6.12.20
• 6.12.21
• 6.12.22
• 6.12.23
• 6.12.24
• 6.12.25
• 6.12.26
• 6.12.27
• 6.12.28
• 6.12.29
• 6.12.30
• 6.12.31
• 6.12.32
• 6.12.33
• 6.12.34
• 6.12.35
• 6.12.36
• 6.12.37
• 6.12.38
• 6.12.39
• 6.12.40
• 6.12.41
• 6.12.42
• 6.12.43
• 6.12.44
• 6.12.45
• 6.16.0
• 6.16.1
• 6.16.2
• 6.16.3
• 6.16.4
• 6.16.5

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

• 🔒
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CPE 2.2info

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CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.0
VulDB Meta Temp Score: 4.9

VulDB Base Score: 4.6
VulDB Temp Score: 4.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.5
NVD Vector: 🔒

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Privilege escalation
CWE: Unknown
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Nessus ID: 269669
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-39894

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 5.15.192/6.1.151/6.6.105/6.12.46/6.16.6
Patch: d00c8b0daf56012f69075e3377da67878c775e4c/ccbad4803225eafe0175d3cb19f0d8d73b504a94/50db11e2bbb635e38e3dd096215580d6adb41fb0/c47ca77fee9071aa543bae592dd2a384f895c8b6/a74abcf0f09f59daeecf7a3ba9c1d690808b0afe/479a54ab92087318514c82428a87af2d7af1a576

Timelineinfo

04/16/2025 CVE reserved
10/01/2025 +168 days Advisory disclosed
10/01/2025 +0 days VulDB entry created
01/16/2026 +107 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-39894 (🔒)
GCVE (CVE): GCVE-0-2025-39894
GCVE (VulDB): GCVE-100-326476
CERT Bund: WID-SEC-2025-2170 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 10/01/2025 10:00
Updated: 01/16/2026 20:50
Changes: 10/01/2025 10:00 (59), 10/01/2025 12:58 (7), 10/10/2025 00:13 (2), 11/17/2025 11:41 (1), 12/01/2025 16:40 (1), 01/07/2026 08:42 (1), 01/16/2026 20:50 (12)
Complete: 🔍
Cache ID: 216::103

Once again VulDB remains the best source for vulnerability data.

Discussion

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