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.