In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE
conn->preauth_info is shared connection state (struct
preauth_integrity_info, kmalloc-96) that is allocated and freed by the
SMB2 NEGOTIATE handler and read by the response send path.
smb2_handle_negotiate() allocates conn->preauth_info, and on a
deassemble_neg_contexts() failure kfrees it and sets it to NULL. Both the
allocation and the free/NULL happen under ksmbd_conn_lock(conn) (the
connection srv_mutex), which is held across the whole handler body.
The response send path smb3_preauth_hash_rsp(), called from the send:
block of __handle_ksmbd_work(), reads conn->preauth_info and dereferences
conn->preauth_info->Preauth_HashValue (via
ksmbd_gen_preauth_integrity_hash()) without taking conn_lock. When a
client drives two SMB2 NEGOTIATE requests on the same connection, one
worker can free conn->preauth_info on the failing-negotiate path while a
concurrent send-path worker is reading it, producing a slab
use-after-free read (KASAN-confirmed).
The send-path read tested conn->preauth_info for NULL but raced with the
free that occurs between the NULL check and the dereference, so the NULL
guard alone does not close the window.
Serialize the NEGOTIATE-branch read in smb3_preauth_hash_rsp() under
ksmbd_conn_lock(conn) and re-check conn->preauth_info inside the lock.
Because the negotiate handler holds conn_lock across its kfree + NULL
assignment, a reader that also takes conn_lock either runs fully before
the allocation or fully after the NULL store, and can never observe the
freed-but-not-yet-NULLed pointer. ksmbd_gen_preauth_integrity_hash()
takes no locks itself (it only computes a SHA-512 over the buffer), so
no lock-ordering inversion is introduced, and conn_lock is a sleepable
mutex which is safe on this send path (it already performs network I/O).
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 9.8
AV:N - The bug is in ksmbd's SMB2 NEGOTIATE handler reachable by any remote client over TCP port 445 without local access; exploitation requires only crafted SMB 3.1.1 negotiate packets on an established network connection.
AC:L - The attacker controls both sides of the race by pipelining two SMB2 NEGOTIATE requests on the same connection, with one crafted to fail deassemble_neg_contexts() and free preauth_info while the other is in the response send path; KASAN-confirmed UAF with no uncontrollable timing.
PR:N - SMB2 NEGOTIATE is processed before any authentication or session establishment; smb2_check_user_session explicitly exempts NEGOTIATE from session validation, so an unauthenticated remote attacker can reach the vulnerable code path.
UI:N - Exploitation requires only network packets sent by the attacker to an exposed ksmbd instance; no victim user action such as mounting a share or opening a file is needed.
S:U - Successful exploitation compromises kernel memory on the SMB server host itself; this is standard in-kernel memory corruption without crossing a VM, container, or IOMMU security boundary to a separate authority.
C:H - KASAN-confirmed slab use-after-free read of conn->preauth_info (kmalloc-96) via Preauth_HashValue and Preauth_HashId dereference; UAF on attacker-influenced freed heap memory enables arbitrary kernel memory disclosure through heap grooming.
I:H - The UAF corrupts kernel heap state on a network-facing pre-auth path; freed preauth_integrity_info objects can be reallocated via heap spraying to obtain arbitrary write or control-flow hijack primitives beyond the immediate hash-buffer access.
A:H - Concurrent UAF read of freed conn->preauth_info during smb3_preauth_hash_rsp() causes kernel oops or panic (KASAN-confirmed); even without full exploitation the race reliably triggers high-severity denial of service on the server.
| Attack Vector |
Network |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
None |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:N - The bug is in ksmbd's SMB2 NEGOTIATE handler reachable by any remote client over TCP port 445 without local access; exploitation requires only crafted SMB 3.1.1 negotiate packets on an established network connection.
AC:L - The attacker controls both sides of the race by pipelining two SMB2 NEGOTIATE requests on the same connection, with one crafted to fail deassemble_neg_contexts() and free preauth_info while the other is in the response send path; KASAN-confirmed UAF with no uncontrollable timing.
PR:N - SMB2 NEGOTIATE is processed before any authentication or session establishment; smb2_check_user_session explicitly exempts NEGOTIATE from session validation, so an unauthenticated remote attacker can reach the vulnerable code path.
UI:N - Exploitation requires only network packets sent by the attacker to an exposed ksmbd instance; no victim user action such as mounting a share or opening a file is needed.
S:U - Successful exploitation compromises kernel memory on the SMB server host itself; this is standard in-kernel memory corruption without crossing a VM, container, or IOMMU security boundary to a separate authority.
C:H - KASAN-confirmed slab use-after-free read of conn->preauth_info (kmalloc-96) via Preauth_HashValue and Preauth_HashId dereference; UAF on attacker-influenced freed heap memory enables arbitrary kernel memory disclosure through heap grooming.
I:H - The UAF corrupts kernel heap state on a network-facing pre-auth path; freed preauth_integrity_info objects can be reallocated via heap spraying to obtain arbitrary write or control-flow hijack primitives beyond the immediate hash-buffer access.
A:H - Concurrent UAF read of freed conn->preauth_info during smb3_preauth_hash_rsp() causes kernel oops or panic (KASAN-confirmed); even without full exploitation the race reliably triggers high-severity denial of service on the server.
CVSS 3.1