Kernel use-after-free via malformed SMB1 response
Published Sep 11, 2026 · Updated Sep 11, 2026
Use-after-free in the Linux SMB1 client allows remote attackers controlling an SMB server to trigger freed-buffer reuse via malformed replies. After a valid primary TRANSACT2 response, cifs_check_trans2() rejects a malformed secondary response, but handle_mid() overwrites mid->resp_buf and leaves server->smallbuf or server->bigbuf dangling. The client must connect to an attacker-controlled SMB1 server; the demultiplexing thread then reuses the freed buffer for the next packet.
Summary
What happened
Use-after-free in the Linux SMB1 client allows remote attackers controlling an SMB server to trigger freed-buffer reuse via malformed replies. After a valid primary TRANSACT2 response, cifs_check_trans2() rejects a malformed secondary response, but handle_mid() overwrites mid->resp_buf and leaves server->smallbuf or server->bigbuf dangling. The client must connect to an attacker-controlled SMB1 server; the demultiplexing thread then reuses the freed buffer for the next packet.
The record
- CVE
- CVE-2026-89637
- Published
- Sep 11, 2026
- Updated
- Sep 11, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux
- Classifications
- T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 11, 2026CVE publishedPublication date reported by the CVE source.
- Sep 11, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=316cf94a910f6f93d43cc574359d163ccae098a3 <5e6533a683f6a851158d9f33fb4ea8f4f25d7f84
- Affected versionversion=316cf94a910f6f93d43cc574359d163ccae098a3 <730d0bb19507b9e19c2fe5343109ac618e2fbce5
- Affected versionversion=316cf94a910f6f93d43cc574359d163ccae098a3 <9eed72e9534b10a6d9f8f5146feff3db53aebdba
- Affected versionversion=3.6
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What is affected?
Published CVSS scores
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Attacks
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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