Linux Kernel up to 6.18.50/7.2.3 SMB client /proc/fs/cifs/DebugData CIFSTCon nativeFileSystem memory corruption

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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6.0$0-$5k0.00+

Summaryinfo

A vulnerability, which was classified as critical, has been found in Linux Kernel up to 6.18.50/7.2.3. This vulnerability affects the function CIFSTCon of the file /proc/fs/cifs/DebugData of the component SMB client. The manipulation of the argument nativeFileSystem leads to memory corruption. This vulnerability is uniquely identified as CVE-2026-89631. The attack is possible to be carried out remotely. No exploit exists. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Linux Kernel up to 6.18.50/7.2.3. This issue affects the function CIFSTCon of the file /proc/fs/cifs/DebugData of the component SMB client. The manipulation of the argument nativeFileSystem with an unknown input leads to a memory corruption vulnerability. Using CWE to declare the problem leads to CWE-119. The product performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: smb: client: reject a tree connect response whose byte count is too small CIFSTCon() bounds its strnlen() over the byte area with the server's ByteCount minus two, which for ByteCount 0 or 1 goes negative as an int and converts to a huge size_t. The later subtraction wraps the __u16 bytes_left, and that is what bounds cifs_strndup_from_utf16(): a bound of up to 65535 against a ~16 KB cifs_req_poolp object runs off the end of the slab object, and the bytes reach userspace through tcon->nativeFileSystem in /proc/fs/cifs/DebugData. Reject a byte area too small for what the parser consumes. Two bytes is the least it can consume, and no conformant response carries fewer. The new trace point is the 129th smb_eio_trace entry, which __mode(byte) cannot represent, so the attribute goes with it.

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2026-89631 since 09/11/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/12/2026).

Upgrading to version 6.18.51, 7.2.4 or 7.3-rc1 eliminates this vulnerability. Applying the patch 3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d/411e484fe71a7f1028de617447edad9cb6d9d68a/65deb18359341141d37dc86fc7853511be3c87a7 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.3
VulDB Meta Temp Score: 6.0

VulDB Base Score: 6.3
VulDB Temp Score: 6.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

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

Exploitinginfo

Class: Memory corruption
CWE: CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

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

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Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.18.51/7.2.4/7.3-rc1
Patch: 3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d/411e484fe71a7f1028de617447edad9cb6d9d68a/65deb18359341141d37dc86fc7853511be3c87a7

Timelineinfo

09/11/2026 CVE reserved
09/12/2026 +1 days Advisory disclosed
09/12/2026 +0 days VulDB entry created
09/12/2026 +0 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-89631 (🔒)
GCVE (CVE): GCVE-0-2026-89631
GCVE (VulDB): GCVE-100-402977

Entryinfo

Created: 09/12/2026 02:21
Changes: 09/12/2026 02:21 (61)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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