CVE-2026-89637

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.