What is CVE-2026-89637?

CVE-2026-89637 is a Critical severity Linux kernel vulnerability with a CVSS score of 9.8 out of 10, affecting Linux kernel versions from 3.6 onward and patched in 6.18.51, 7.2.4 and 7.3-rc1. CVE-2026-89637 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

What is the CVSS score for CVE-2026-89637?

CVE-2026-89637 has a CVSS score of 9.8 out of 10, rated Critical severity. The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Is there a patch available for CVE-2026-89637?

Yes, CVE-2026-89637 has been patched. Fixed versions include 6.18.51, 7.2.4 and 7.3-rc1. If you are running Linux kernel 3.6 or later up to the fix versions, apply the relevant patch for your kernel branch.

Is CVE-2026-89637 actively exploited?

CVE-2026-89637 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

CVE-2026-89637

Critical

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2 When a valid primary TRANSACT2 response has been received (mid->resp_buf set, mid->multiRsp true) and a subsequent secondary response causes cifs_check_trans2() to return false -- either because the SMB header is invalid (malformed != 0) or because check2ndT2() rejects the PDU -- handle_mid() overwrites mid->resp_buf with the new buffer (leaking the primary buffer) and, because mid->multiRsp is set, skips the server->smallbuf/bigbuf NULL-out. When the user thread frees mid->resp_buf, server->smallbuf or server->bigbuf is left dangling; the demux thread reuses it for the next packet, resulting in a use-after-free. Combine both early-exit conditions and, when mid->multiRsp is already set, abort the pending transaction inline: set multiEnd, call dequeue_mid() with malformed=true, and return true so handle_mid() exits without touching mid->resp_buf or the server buffer pointers.

Package Linux Kernel

Published 2026-09-11

Last modified 2026-09-13

CVSS version 3.1

Patch available

Yes

CVSS 3.1 score

9.8

out of 10

Critical

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Vector string

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected versions

Linux kernel versions 3.6 and later are affected. Fixed in 6.18.51, 7.2.4, 7.3-rc1 and their respective stable series.

Affected from

≥ 3.6

Fixed in

✓ 6.18.51 6.18.x ✓ 7.2.4 7.2.x ✓ 7.3-rc1

References

3 total

Details

CVE ID CVE-2026-89637

Severity Critical

CVSS score 9.8 / 10

CVSS version 3.1

Published 2026-09-11

Modified 2026-09-13

KEV No

Patch

Yes

Package linux

Frequently asked questions

What is CVE-2026-89637?

CVE-2026-89637 is a Critical severity Linux kernel vulnerability with a CVSS score of 9.8 out of 10 . It affects Linux kernel versions from 3.6 onward and has been patched in 6.18.51, 7.2.4 and 7.3-rc1. CVE-2026-89637 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.
What is the CVSS score for CVE-2026-89637?

CVE-2026-89637 has a CVSS score of 9.8 out of 10, rated Critical severity (CVSS 3.1). The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
Is there a patch available for CVE-2026-89637?

Yes. CVE-2026-89637 has been patched. Fixed versions include 6.18.51, 7.2.4 and 7.3-rc1. If you are running Linux kernel 3.6 or later up to the fix versions, apply the relevant patch for your kernel branch.
Is CVE-2026-89637 actively exploited?

No. CVE-2026-89637 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.