{"id":"CVE-2026-72422","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-72422","summary":"ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE\n\nconn->preauth_info is shared connection state (struct\npreauth_integrity_info, kmalloc-96) that is allocated and freed by the\nSMB2 NEGOTIATE handler and read by the response send path.\n\nsmb2_handle_negotiate() allocates conn->preauth_info, and on a\ndeassemble_neg_contexts() failure kfrees it and sets it to NULL. Both the\nallocation and the free/NULL happen under ksmbd_conn_lock(conn) (the\nconnection srv_mutex), which is held across the whole handler body.\n\nThe response send path smb3_preauth_hash_rsp(), called from the send:\nblock of __handle_ksmbd_work(), reads conn->preauth_info and dereferences\nconn->preauth_info->Preauth_HashValue (via\nksmbd_gen_preauth_integrity_hash()) without taking conn_lock. When a\nclient drives two SMB2 NEGOTIATE requests on the same connection, one\nworker can free conn->preauth_info on the failing-negotiate path while a\nconcurrent send-path worker is reading it, producing a slab\nuse-after-free read (KASAN-confirmed).\n\nThe send-path read tested conn->preauth_info for NULL but raced with the\nfree that occurs between the NULL check and the dereference, so the NULL\nguard alone does not close the window.\n\nSerialize the NEGOTIATE-branch read in smb3_preauth_hash_rsp() under\nksmbd_conn_lock(conn) and re-check conn->preauth_info inside the lock.\nBecause the negotiate handler holds conn_lock across its kfree + NULL\nassignment, a reader that also takes conn_lock either runs fully before\nthe allocation or fully after the NULL store, and can never observe the\nfreed-but-not-yet-NULLed pointer. ksmbd_gen_preauth_integrity_hash()\ntakes no locks itself (it only computes a SHA-512 over the buffer), so\nno lock-ordering inversion is introduced, and conn_lock is a sleepable\nmutex which is safe on this send path (it already performs network I/O).","published":"2026-08-15T05:56:41.090Z","modified":"2026-08-16T03:48:41.511675679Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"5.15.212"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/0c054227479ed7e36ebccb3a558bc0ef698264f6"},{"type":"WEB","url":"https://git.kernel.org/stable/c/16a1ecf39c217e3d164bd32ef2a4f650abc067fa"},{"type":"WEB","url":"https://git.kernel.org/stable/c/1c89da3baa2b1f269178afa87dc30479b8535776"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7470511d085af1c7a043a60e53d52b512d5a10b1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/77bb0bbfcc4e777ca653174689e5e363f8ee63d1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c7bef84740d1d57848c74f6f5b996606e43ea4fe"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d0a469122e7bf8338fec1949fb1e8e1290ed8caa"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72422.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-72422"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-16T03:48:41.511675679Z"}}