Linux Kernel up to 6.6.144/6.12.96/6.18.39/7.1.4 v9fs fs/inode.c v9fs_dec_count toctou

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5.2	$0-$5k	0.96

Summaryinfo

A vulnerability classified as problematic was found in Linux Kernel up to 6.6.144/6.12.96/6.18.39/7.1.4. Affected by this issue is the function v9fs_dec_count of the file fs/inode.c of the component v9fs. The manipulation results in toctou. This vulnerability is known as CVE-2026-72170. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability classified as problematic has been found in Linux Kernel up to 6.6.144/6.12.96/6.18.39/7.1.4. Affected is the function v9fs_dec_count of the file fs/inode.c of the component v9fs. The manipulation with an unknown input leads to a toctou vulnerability. CWE is classifying the issue as CWE-367. The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state. This is going to have an impact on integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: 9p: skip nlink update in cacheless mode to fix WARN_ON v9fs_dec_count() unconditionally calls drop_nlink() on regular files, even when the inode's nlink is already zero. In cacheless mode the client refetches inode metadata from the server (the source of truth) on every operation, so by the time v9fs_remove() returns, the locally cached nlink may already reflect the post-unlink value: 1. Client initiates unlink, server processes it and sets nlink to 0 2. Client refetches inode metadata (nlink=0) before unlink returns 3. Client's v9fs_remove() completes successfully 4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0 This race is easily triggered under heavy unlink workloads, such as stress-ng's unlink stressor, producing the following warning: WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8 Call trace: drop_nlink+0x4c/0xc8 v9fs_remove+0x1e0/0x250 [9p] v9fs_vfs_unlink+0x20/0x38 [9p] vfs_unlink+0x13c/0x258 ... In cacheless mode the server is authoritative and the inode is on its way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count() entirely when neither CACHE_META nor CACHE_LOOSE is set, which both avoids the warning and removes a class of nlink races (two concurrent unlinkers observing nlink > 0 and both calling drop_nlink()) that an nlink == 0 guard alone would only narrow rather than close.

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2026-72170 since 08/09/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/15/2026).

Upgrading to version 6.6.145, 6.12.97, 6.18.40, 7.1.5 or 7.2-rc1 eliminates this vulnerability. Applying the patch a5a682b016ef5b5384e28f6d652d47a8f8e73d37/de79c3f3643841b8659a71958df7cf2a66bfd409/8d610017c992de705b304d3d727a6e3a86af6149/8faccac11e1369adddf5d80f4a45af93f13b2e1a/574aa0b4799470ac814479f1138d19efe6262255 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.6.144
• 6.12.0
• 6.12.1
• 6.12.2
• 6.12.3
• 6.12.4
• 6.12.5
• 6.12.6
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• 6.12.89
• 6.12.90
• 6.12.91
• 6.12.92
• 6.12.93
• 6.12.94
• 6.12.95
• 6.12.96
• 6.18.0
• 6.18.1
• 6.18.2
• 6.18.3
• 6.18.4
• 6.18.5
• 6.18.6
• 6.18.7
• 6.18.8
• 6.18.9
• 6.18.10
• 6.18.11
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• 6.18.33
• 6.18.34
• 6.18.35
• 6.18.36
• 6.18.37
• 6.18.38
• 6.18.39
• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3
• 7.1.4

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.4
VulDB Meta Temp Score: 5.2

VulDB Base Score: 5.4
VulDB Temp Score: 5.2
VulDB Vector: 🔒
VulDB Reliability: 🔍

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: Toctou
CWE: CWE-367 / CWE-362
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.6.145/6.12.97/6.18.40/7.1.5/7.2-rc1
Patch: a5a682b016ef5b5384e28f6d652d47a8f8e73d37/de79c3f3643841b8659a71958df7cf2a66bfd409/8d610017c992de705b304d3d727a6e3a86af6149/8faccac11e1369adddf5d80f4a45af93f13b2e1a/574aa0b4799470ac814479f1138d19efe6262255

Timelineinfo

08/09/2026 CVE reserved
08/15/2026 +6 days Advisory disclosed
08/15/2026 +0 days VulDB entry created
08/15/2026 +0 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-72170 (🔒)
GCVE (CVE): GCVE-0-2026-72170
GCVE (VulDB): GCVE-100-390600

Entryinfo

Created: 08/15/2026 13:12
Changes: 08/15/2026 13:12 (60)
Complete: 🔍
Cache ID: 216::103

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Discussion

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