---
cve: "CVE-2026-89637"
severity: "CRITICAL"
cvss: 9.8
epss: "57.3%"
vendor: "Linux"
kev: false
exploited: false
published: "2026-09-11 20:19:49"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-09-15T09:04:25+02:00"
---

# CVE-2026-89637

> 9.8 CRITICAL

## Beschreibung

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.

## CVSS-Vektor

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

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Hoch | bad |
| I Integrität | Hoch | bad |
| A Verfügbarkeit | Hoch | bad |

## Patch verfügbar (OSV)

- Kernel ≥ 6.18.51
- Kernel ≥ 7.2.4

## Referenzen

- <https://git.kernel.org/stable/c/5e6533a683f6a851158d9f33fb4ea8f4f25d7f84>
- <https://git.kernel.org/stable/c/730d0bb19507b9e19c2fe5343109ac618e2fbce5>
- <https://git.kernel.org/stable/c/9eed72e9534b10a6d9f8f5146feff3db53aebdba>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-89637) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_