Linux Kernel up to 6.1.146/6.6.99/6.12.39/6.15.7 netfilter __nf_conntrack_find_get allocation of resources

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Summaryinfo

A vulnerability was found in Linux Kernel up to 6.1.146/6.6.99/6.12.39/6.15.7. It has been rated as critical. This affects the function __nf_conntrack_find_get of the component netfilter. The manipulation leads to allocation of resources. This vulnerability is documented as CVE-2025-38472. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Linux Kernel up to 6.1.146/6.6.99/6.12.39/6.15.7. This issue affects the function __nf_conntrack_find_get of the component netfilter. The manipulation with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Impacted is availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack: fix crash due to removal of uninitialised entry A crash in conntrack was reported while trying to unlink the conntrack entry from the hash bucket list: [exception RIP: __nf_ct_delete_from_lists+172] [..] #7 [ff539b5a2b043aa0] nf_ct_delete at ffffffffc124d421 [nf_conntrack] #8 [ff539b5a2b043ad0] nf_ct_gc_expired at ffffffffc124d999 [nf_conntrack] #9 [ff539b5a2b043ae0] __nf_conntrack_find_get at ffffffffc124efbc [nf_conntrack] [..] The nf_conn struct is marked as allocated from slab but appears to be in a partially initialised state: ct hlist pointer is garbage; looks like the ct hash value (hence crash). ct->status is equal to IPS_CONFIRMED|IPS_DYING, which is expected ct->timeout is 30000 (=30s), which is unexpected. Everything else looks like normal udp conntrack entry. If we ignore ct->status and pretend its 0, the entry matches those that are newly allocated but not yet inserted into the hash: - ct hlist pointers are overloaded and store/cache the raw tuple hash - ct->timeout matches the relative time expected for a new udp flow rather than the absolute 'jiffies' value. If it were not for the presence of IPS_CONFIRMED, __nf_conntrack_find_get() would have skipped the entry. Theory is that we did hit following race: cpu x cpu y cpu z found entry E found entry E E is expired <preemption> nf_ct_delete() return E to rcu slab init_conntrack E is re-inited, ct->status set to 0 reply tuplehash hnnode.pprev stores hash value. cpu y found E right before it was deleted on cpu x. E is now re-inited on cpu z. cpu y was preempted before checking for expiry and/or confirm bit. ->refcnt set to 1 E now owned by skb ->timeout set to 30000 If cpu y were to resume now, it would observe E as expired but would skip E due to missing CONFIRMED bit. nf_conntrack_confirm gets called sets: ct->status |= CONFIRMED This is wrong: E is not yet added to hashtable. cpu y resumes, it observes E as expired but CONFIRMED: <resumes> nf_ct_expired() -> yes (ct->timeout is 30s) confirmed bit set. cpu y will try to delete E from the hashtable: nf_ct_delete() -> set DYING bit __nf_ct_delete_from_lists Even this scenario doesn't guarantee a crash: cpu z still holds the table bucket lock(s) so y blocks: wait for spinlock held by z CONFIRMED is set but there is no guarantee ct will be added to hash: "chaintoolong" or "clash resolution" logic both skip the insert step. reply hnnode.pprev still stores the hash value. unlocks spinlock return NF_DROP <unblocks, then crashes on hlist_nulls_del_rcu pprev> In case CPU z does insert the entry into the hashtable, cpu y will unlink E again right away but no crash occurs. Without 'cpu y' race, 'garbage' hlist is of no consequence: ct refcnt remains at 1, eventually skb will be free'd and E gets destroyed via: nf_conntrack_put -> nf_conntrack_destroy -> nf_ct_destroy. To resolve this, move the IPS_CONFIRMED assignment after the table insertion but before the unlock. Pablo points out that the confirm-bit-store could be reordered to happen before hlist add resp. the timeout fixup, so switch to set_bit and before_atomic memory barrier to prevent this. It doesn't matter if other CPUs can observe a newly inserted entry right before the CONFIRMED bit was set: Such event cannot be distinguished from above "E is the old incarnation" case: the entry will be skipped. Also change nf_ct_should_gc() to first check the confirmed bit. The gc sequence is: 1. Check if entry has expired, if not skip to next entry 2. Obtain a reference to the expired entry. 3. Call nf_ct_should_gc() to double-check step 1. nf_ct_should_gc() is thus called only for entries that already failed an expiry check. After this patch, once the confirmed bit check pas ---truncated---

It is possible to read the advisory at git.kernel.org. The identification of this vulnerability is CVE-2025-38472 since 04/16/2025. The exploitation is known to be difficult. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 251301 (Linux Distros Unpatched Vulnerability : CVE-2025-38472), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.1.147, 6.6.100, 6.12.40 or 6.15.8 eliminates this vulnerability. Applying the patch a47ef874189d47f934d0809ae738886307c0ea22/76179961c423cd698080b5e4d5583cf7f4fcdde9/fc38c249c622ff5e3011b8845fd49dbfd9289afc/938ce0e8422d3793fe30df2ed0e37f6bc0598379/2d72afb340657f03f7261e9243b44457a9228ac7 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 (251301) and CERT Bund (WID-SEC-2025-1665). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

  • Google Container-Optimized OS
  • Debian Linux
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • IBM QRadar SIEM
  • SUSE openSUSE
  • RESF Rocky Linux
  • Dell Avamar
  • NetApp ActiveIQ Unified Manager
  • Dell PowerProtect Data Domain
  • Open Source Linux Kernel
  • Dell NetWorker
  • Dell Secure Connect Gateway
  • IBM Security Verify Access

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.1
VulDB Meta Temp Score: 5.0

VulDB Base Score: 4.8
VulDB Temp Score: 4.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.5
NVD Vector: 🔒

CVSSv2info

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

Exploitinginfo

Class: Allocation of resources
CWE: CWE-770 / CWE-400 / CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 251301
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-38472

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.1.147/6.6.100/6.12.40/6.15.8
Patch: a47ef874189d47f934d0809ae738886307c0ea22/76179961c423cd698080b5e4d5583cf7f4fcdde9/fc38c249c622ff5e3011b8845fd49dbfd9289afc/938ce0e8422d3793fe30df2ed0e37f6bc0598379/2d72afb340657f03f7261e9243b44457a9228ac7

Timelineinfo

04/16/2025 CVE reserved
07/28/2025 +103 days Advisory disclosed
07/28/2025 +0 days VulDB entry created
01/25/2026 +181 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-38472 (🔒)
GCVE (CVE): GCVE-0-2025-38472
GCVE (VulDB): GCVE-100-317891
CERT Bund: WID-SEC-2025-1665 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 07/28/2025 14:51
Updated: 01/25/2026 13:46
Changes: 07/28/2025 14:51 (59), 08/17/2025 20:23 (7), 08/18/2025 12:24 (1), 08/19/2025 12:13 (2), 08/20/2025 12:17 (1), 08/26/2025 16:03 (1), 09/30/2025 11:43 (1), 10/18/2025 10:01 (1), 11/02/2025 00:36 (1), 11/16/2025 19:16 (1), 12/23/2025 02:41 (13), 01/25/2026 13:46 (1)
Complete: 🔍
Cache ID: 216::103

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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