CVE-2026-72422
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk49th percentile - higher than 49% of all known CVEs
Summary
In the Linux kernel, the ksmbd (SMB server) module has a use-after-free vulnerability in the conn->preauth_info structure during concurrent SMB2 NEGOTIATE requests. One thread can free the memory while another thread in the response send path still uses it, leading to a use-after-free read (confirmed by KASAN).
Risk Assessment
An attacker could exploit this vulnerability to cause a system crash (kernel panic) or potentially escalate privileges in environments with ksmbd enabled. However, this requires access to an SMB connection and sending two concurrent NEGOTIATE requests.
Recommendation
Apply the official Linux kernel patch that serializes the conn->preauth_info read under ksmbd_conn_lock. If the kernel cannot be updated immediately, consider disabling the ksmbd module or restricting access to the SMB service.
Other vulnerabilities in Linux kernel
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Original NVD description (English source)
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).
Vulnerability data from NVD (NIST) · CISA KEV · EPSS