CVE-2026-89635
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk45th percentile - higher than 45% of all known CVEs
Summary
In the Linux kernel, the ksmbd_reopen_durable_fd() function rebinds every detached oplock on an inode to the reconnecting session instead of only the oplock owned by the reopened file. This allows one session to adopt another session's oplock, and when the adopting session is destroyed, a use-after-free occurs. The vulnerability is reachable with the default durable-handle and oplock configuration when two sessions open the same file with distinct AppInstanceIds.
Risk Assessment
An authenticated user can trigger a slab-use-after-free in the kernel, potentially causing a kernel panic or, in the worst case, enabling code execution in kernel context. The risk affects SMB file servers using ksmbd with the default durable-handle and oplock configuration.
Recommendation
Update the Linux kernel to a version containing the fix that constrains the rebind loop to the oplock owned by the file being reopened. Until the patch is applied, consider disabling durable handles or oplocks on SMB shares if they are not required.
Other vulnerabilities in Linux kernel (ksmbd)
See all- CVE-2026-89788Critical
In the Linux kernel, the ksmbd module contains a use-after-free vulnerability in smb2_tree_connect(). A newly created tree connection is published in the session and then used by the handler, while a concurrent session logoff can free the object before the handler finishes.
- CVE-2026-80926Critical
A use-after-free vulnerability was fixed in the Linux kernel's ksmbd oplock break notification mechanism. The smb2_oplock_break_noti() function read the opinfo->conn pointer without locking and dereferenced it after sleeping allocations, allowing a race with durable handle teardown to access a freed connection. The flaw is reachable by any authenticated client holding a durable batch oplock.
- CVE-2026-43376Critical
A vulnerability has been identified in the Linux kernel within ksmbd, related to a use-after-free error due to immediate freeing of the oplock_info structure. This issue occurs when the pointer is nullified without a grace period delay in RCU, allowing access to already freed memory.
- CVE-2026-43185Critical
The ksmbd module in the Linux kernel has a signedness bug in smb_direct_prepare_negotiation(). An unsigned __u32 value from preferred_send_size is cast to a signed int before computing min_t(int, ...), so a malicious value of 0x80000000 is treated as smaller than max_recv_size and used to set the maximum allowed receive size. By sending a second message with a large value (>1420 bytes), the attacker can achieve a heap buffer overflow.
- CVE-2026-23428Critical
A use-after-free vulnerability exists in the Linux kernel ksmbd module involving the share_conf object in compound requests. smb2_get_ksmbd_tcon() reuses work->tcon without validating tcon->t_state, so after an earlier SMB2_TREE_DISCONNECT frees share_conf, subsequent commands dereference the freed memory.
- CVE-2023-54203Critical
In the Linux kernel, a vulnerability in the ksmbd module leads to a slab-out-of-bounds read in the init_smb2_rsp_hdr function. The issue occurs when an SMB1 mount attempt fails and the ksmbd server incorrectly handles SMB1 negotiation as an SMB2 operation, causing an out-of-bounds memory read.
- CVE-2023-38432Critical
An issue was discovered in the Linux kernel before 6.3.10 related to the validation of command payload size in ksmbd, leading to an out-of-bounds read.
- CVE-2023-38431Critical
An issue was discovered in the Linux kernel before 6.3.8 related to the lack of validation of the NetBIOS header's length in relation to SMB header sizes in ksmbd. This leads to an out-of-bounds read.
- CVE-2023-38427Critical
An issue was discovered in the Linux kernel before 6.3.8 related to integer underflow and out-of-bounds read in the deassemble_neg_contexts function in fs/smb/server/smb2pdu.c in ksmbd.
- CVE-2026-98420Low risk· EPSS 14%
In the Linux kernel, the ksmbd (SMB server) module mishandles SMB2 session expiration. The ksmbd_session_register() function destroyed valid sessions after ten seconds of inactivity whenever a client started another SessionSetup exchange, confusing Session.IdleTime with Session.ExpirationTime. This invalidated tree connects and caused mapped drives to fail with STATUS_NETWORK_NAME_DELETED.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: ksmbd: only rebind the reopened file's own oplock on durable reconnect ksmbd_reopen_durable_fd() walks the inode's m_op_list and rebinds every detached oplock to the reconnecting session: list_for_each_entry_rcu(op, &ci->m_op_list, op_entry, lockdep_is_held(&ci->m_lock)) { if (op->conn) continue; op->conn = ksmbd_conn_get(fp->conn); op->sess = work->sess; } The only key is op->conn == NULL, which every detached durable handle on that inode matches, not just the one owned by fp. When two sessions hold durable handles on the same file and both disconnect, reconnecting one of them adopts the other session's oplock: op->sess is overwritten with the reconnecting session without taking a reference on it, while op->conn pins the connection. The sibling teardown path, session_fd_check(), keys on the identity of the connection being torn down (op->conn == conn) rather than on shared state, and so does not have this problem. Once the adopting session is destroyed, ksmbd_session_destroy() frees it while the foreign oplock still points at it. The reader in ksmbd_close_fd_app_instance_id() validates only opinfo->conn, which is still live thanks to the reference taken above, and then dereferences the stale session: if (!opinfo->conn) { up_read(&fp->f_ci->m_lock); goto out; } ft = &opinfo->sess->file_table; write_lock(&ft->lock); BUG: KASAN: slab-use-after-free in _raw_write_lock+0x74/0xd0 Write of size 4 at addr ffff88810a970528 by task kworker/0:0/9 Workqueue: ksmbd-io handle_ksmbd_work Call Trace: _raw_write_lock+0x74/0xd0 ksmbd_close_fd_app_instance_id+0x183/0x410 smb2_open+0x1346/0x4430 handle_ksmbd_work+0x2bb/0x7b0 Reached from an authenticated session against a share with the default durable-handle and oplock configuration: two sessions open the same file with a durable-v2 handle and an RH lease under distinct AppInstanceIds, both log off, one reconnects with DH2C, and a later durable-v2 create carrying the other AppInstanceId walks into the freed session. Constrain the loop to the oplock owned by the file being reopened.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS