CVE-2026-31609

smb: client: avoid double-free in smbd_free_send_io() after smbd_send_batch_flush()

Published Apr 24, 2026 CVSS 3.1 · 9.8 Critical EPSS < 1% KEV · Not listed

Description

In the Linux kernel, the following vulnerability has been resolved:

smb: client: avoid double-free in smbd_free_send_io() after smbd_send_batch_flush()

smbd_send_batch_flush() already calls smbd_free_send_io(),
so we should not call it again after smbd_post_send()
moved it to the batch list.

Analysis

Technical impact

The Linux kernel’s SMB client has a double‑free vulnerability in the smbd_send_batch_flush() routine, which calls smbd_free_send_io() a second time after it has already been freed. This is a classic double‑free flaw (CWE‑415) that can cause heap corruption in the kernel, potentially leading to arbitrary code execution with kernel privileges.

Affected Systems

All Linux kernel releases that contain the SMB client code before the fix are impacted. Specific version ranges are not provided, so any kernel built from source or distributed before the commit that removes the double‑free will be vulnerable. The issue applies to the generic Linux kernel across all distributions.

Risk and Exploitability

The CVSS score of 9.8 indicates a critical vulnerability, while an EPSS score of less than 1% suggests a low current exploitation probability. The flaw is not listed in CISA’s KEV catalog. Based on the description, it is inferred that an attacker could trigger this double‑free (CWE‑415) by sending specially crafted SMB traffic to a vulnerable client, potentially causing memory corruption and kernel privilege escalation.

Affected Products

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
`cca0526ef2344cab6944d7f441fc24e152da031b`	affected	< a9940dcbe5cb92482c04efc7341039ddf7dbf607
`37b5c06956183b65e6808b509cf637632016cdf7`	affected	< 22b7c1c619d808aec4cad3dc42103345e370d107
`21538121efe6c8c5b51c742fa02cbe820bc48714`	affected	< f9a162c2bbcd0ac85bd07c5b37cf20286048b65c
`21538121efe6c8c5b51c742fa02cbe820bc48714`	affected	< 27b7c3e916218b5eb2ee350211140e961bfc49be
`6.18.11`	affected	< 6.18.24
`6.19.1`	affected	< 6.19.14

Linux

affected

Version	Status	Constraints
`7.0`	affected	—
`0`	unaffected	< 7.0
`6.18.24`	unaffected	≤ 6.18.*
`6.19.14`	unaffected	≤ 6.19.*
`7.0.1`	unaffected	≤ 7.0.*
`7.1`	unaffected	≤ *

Configuration 1 [-]

OR	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::

No data.

Vendor Product Versions

Linux

Linux Kernel

Version	Status	Scheme	Platform
`[cca0526ef2344cab6944d7f441fc24e152da031b,a9940dcbe5cb92482c04efc7341039ddf7dbf607)`	affected	code_commit	—
`[37b5c06956183b65e6808b509cf637632016cdf7,22b7c1c619d808aec4cad3dc42103345e370d107)`	affected	code_commit	—
`[21538121efe6c8c5b51c742fa02cbe820bc48714,f9a162c2bbcd0ac85bd07c5b37cf20286048b65c)`	affected	code_commit	—
`[21538121efe6c8c5b51c742fa02cbe820bc48714,27b7c3e916218b5eb2ee350211140e961bfc49be)`	affected	code_commit	—

Linux

Linux Kernel

Version	Status	Scheme	Platform
`7.0`	affected	generic	—
`[0,7.0)`	unaffected	semver	—
`[6.18.24,6.19.0)`	unaffected	semver	—
`[6.19.14,6.20.0)`	unaffected	semver	—
`[7.0.1,7.1.0)`	unaffected	semver	—
`[7.1-rc1,*]`	unaffected	generic	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade to the latest Linux kernel that incorporates the SMB client double‑free fix using your distribution’s package manager or source build.
Reboot the host so the updated kernel image is active.
If a patched kernel is not available and SMB traffic must remain enabled, temporarily disable or restrict SMB services until a newer kernel can be installed.

Generated by OpenCVE AI on April 29, 2026 at 21:38 UTC.

Tracking

Advisories

Source	ID	Title
Ubuntu USN	USN-8488-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8488-2	Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN	USN-8507-1	Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN	USN-8569-1	Linux kernel (HWE) vulnerabilities
Ubuntu USN	USN-8603-1	Linux kernel (Azure) vulnerabilities

Metrics

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

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.

Exploit prediction score: < 1% (0.457% probability within 30 days)

Exploitation none

Automatable yes

Technical Impact total

References

Link	Providers
https://git.kernel.org/stable/c/22b7c1c619d808aec4cad3dc42103345e370d107
https://git.kernel.org/stable/c/27b7c3e916218b5eb2ee350211140e961bfc49be
https://git.kernel.org/stable/c/a9940dcbe5cb92482c04efc7341039ddf7dbf607
https://git.kernel.org/stable/c/f9a162c2bbcd0ac85bd07c5b37cf20286048b65c
https://lore.kernel.org/linux-cve-announce/2026042421-CVE-2026-31609-fc3f@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2026-31609
https://www.cve.org/CVERecord?id=CVE-2026-31609

History

Oct 16, 2026 4:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}`

Apr 29, 2026 5:00 PM Weaknesses updated View changes

Type	Values Removed	Values Added
Weaknesses		CWE-415

Apr 27, 2026 3:00 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics	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'}`	cvssV3_1 `{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}`

Apr 27, 2026 11:30 AM Added references View changes

Type	Values Removed	Values Added
References		https://git.kernel.org/stable/c/27b7c3e916218b5eb2ee350211140e961bfc49be

Apr 25, 2026 12:15 AM Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Weaknesses		CWE-1341
References		https://lore.kernel.org/linux-cve-announce/2026042421-CVE-2026-31609-fc3f@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2026-31609 https://www.cve.org/CVERecord?id=CVE-2026-31609
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 `Moderate`

Apr 24, 2026 3:00 PM Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references View changes

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: smb: client: avoid double-free in smbd_free_send_io() after smbd_send_batch_flush() smbd_send_batch_flush() already calls smbd_free_send_io(), so we should not call it again after smbd_post_send() moved it to the batch list.
Title		smb: client: avoid double-free in smbd_free_send_io() after smbd_send_batch_flush()
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/22b7c1c619d808aec4cad3dc42103345e370d107 https://git.kernel.org/stable/c/a9940dcbe5cb92482c04efc7341039ddf7dbf607 https://git.kernel.org/stable/c/f9a162c2bbcd0ac85bd07c5b37cf20286048b65c