{"id":"CVE-2026-98841","kind":"vulnerability","aliases":["CVE-2026-98841"],"related":[],"title":"Linux kernel: vmgenid driver can panic on early notification interrupt","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nvirt: vmgenid: set driver_data before registering notification handlers\n\nBoth probe paths register their notification handler before assigning\ndriver_data, which the handler dereferences.\n\nIn the devicetree path, the notification IRQ can fire as soon as\ndevm_request_irq() registers the handler: the interrupt may already be\npending at probe time, for example when a VMM injects the\ngeneration-changed notification while restoring a guest from a snapshot\nthat was taken before the driver had probed (Firecracker does exactly\nthis on snapshot restore). The IRQ is also requested with IRQF_SHARED,\nso another device sharing the line can trigger the handler just as\nearly. The handler then calls vmgenid_notify(), which dereferences the\nstill-NULL driver_data and panics:\n\n  Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010\n  CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.18.38+ #1 PREEMPT(none)\n  Hardware name: linux,dummy-virt (DT)\n  pc : vmgenid_notify.isra.0+0x24/0x8c\n  lr : vmgenid_of_irq_handler+0x14/0x34\n  Call trace:\n   vmgenid_notify.isra.0+0x24/0x8c (P)\n   vmgenid_of_irq_handler+0x14/0x34\n   __handle_irq_event_percpu+0x44/0x1bc\n   handle_irq_event+0x4c/0xb4\n   handle_fasteoi_irq+0xf8/0x1f8\n\nThe ACPI path has the same ordering problem: the handler is installed\nwith acpi_install_notify_handler() before driver_data is assigned.\nACPI notifications are dispatched asynchronously from a workqueue, so\nthe window is narrow, but a notification arriving between the two calls\nhits the same NULL dereference.\n\nAssign driver_data before registering the handlers. The state is fully\ninitialized at that point, so the handlers are safe to run. Should\nregistration fail, the probe error path leaves no dangling pointer\nbehind: the driver core clears driver_data in device_unbind_cleanup().","summary":"The Linux vmgenid driver registers its interrupt or notification handler before setting its driver data, so an early notification (for example during a Firecracker snapshot restore or a shared IRQ firing) dereferences a NULL pointer and panics the kernel. The sources describe a denial-of-service crash; they do not describe code execution.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["firecracker","infrastructure","linux-kernel","snapshot-restore","vm-guests"],"not_affected_if":["no-vmgenid-device","no-vmgenid-driver"],"how_to_check":"- `uname -r` to see the running kernel version\n- Check whether the vmgenid driver is in use, for example `lsmod | grep vmgenid` or `ls /sys/bus/platform/drivers/ | grep -i vmgenid`\n- Check whether the kernel includes the fix by looking for the commit 'virt: vmgenid: set driver_data before registering notification handlers' in your distribution's kernel changelog","fix":"- Update the Linux kernel to a release that includes the commit 'virt: vmgenid: set driver_data before registering notification handlers' (fixed version: unknown from sources)\n- Reboot into the patched kernel\n- Check your distribution's advisory for the exact package version: unknown","status":"open","published_at":"2026-10-18T16:17:38+00:00","first_seen_at":"2026-10-23T21:57:17+00:00","triaged_at":"2026-10-25T05:13:13+00:00","updated_at":"2026-10-25T05:13:13+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-10-25T05:13:13Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release that includes the commit 'virt: vmgenid: set driver_data before registering notification handlers' (fixed version: unknown from sources)\n- Reboot into the patched kernel\n- Check your distribution's advisory for the exact package version: unknown","reach":"local","title":"Linux kernel: vmgenid driver can panic on early notification interrupt","impact":"low","summary":"The Linux vmgenid driver registers its interrupt or notification handler before setting its driver data, so an early notification (for example during a Firecracker snapshot restore or a shared IRQ firing) dereferences a NULL pointer and panics the kernel. The sources describe a denial-of-service crash; they do not describe code execution.","category":"infrastructure","nicknames":[],"who_cares":["linux-kernel","vm-guests","firecracker","snapshot-restore"],"confidence":0.6,"needs_auth":"no","worst_case":"Kernel panic, causing denial of service on the guest","analyst_note":"Confirm the affected kernel version range and the fixed stable release from the kernel.org commit or NVD entry for CVE-2026-98841.","how_to_check":"- `uname -r` to see the running kernel version\n- Check whether the vmgenid driver is in use, for example `lsmod | grep vmgenid` or `ls /sys/bus/platform/drivers/ | grep -i vmgenid`\n- Check whether the kernel includes the fix by looking for the commit 'virt: vmgenid: set driver_data before registering notification handlers' in your distribution's kernel changelog","needs_analyst":true,"not_affected_if":["no-vmgenid-device","no-vmgenid-driver"],"who_is_affected":"The bug is in the vmgenid virtual machine generation ID driver, which runs on guests that expose a VM generation ID device, such as Firecracker microVMs using snapshot restore, via devicetree or ACPI. Hosts and guests without this device or driver are not exposed. The sources do not state which kernel versions are vulnerable.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.000768,"input_tokens":3960,"output_tokens":744,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'+0':248C,255C,261C,268C,274C,279C,284C '-2026':12A,15A '-98841':13A,16A '0':225C,227C,247C,260C '0000000000000010':223C '1':229C,235C '6.18.38':234C 'acpi':287C,299C,308C 'address':222C 'alreadi':137C 'also':179C 'anoth':185C 'arriv':324C 'assign':109C,307C,334C 'asynchron':312C 'behind':367C 'call':200C,257C,328C 'chang':152C 'cleanup':377C 'clear':371C 'code':80B 'comm':230C 'core':370C 'cpu':224C 'crash':75B 'cve':11A,14A 'dangl':365C 'data':42B,96C,111C,210C,305C,336C,373C 'denial':72B 'denial-of-servic':71B 'derefer':59B,115C,204C,219C,333C 'describ':69B,79B 'devic':186C,375C 'devicetre':118C 'devm':128C 'dispatch':311C 'driver':4A,31B,41B,95C,110C,166C,209C,304C,335C,369C,372C 'dt':244C 'dummi':242C 'dummy-virt':241C 'earli':8A,45B,196C 'error':361C 'event':272C,278C 'exact':171C 'exampl':48B,144C 'execut':81B 'fail':358C 'fasteoi':282C 'fire':58B,124C 'firecrack':17B,51B,169C 'follow':87C 'fulli':344C 'generat':151C 'generation-chang':150C 'guest':27B,157C 'handl':215C,270C,276C,281C 'handler':37B,100C,107C,114C,133C,193C,198C,254C,267C,295C,302C,340C,351C 'hardwar':238C 'hit':329C 'infrastructur':18B 'initi':345C 'inject':148C 'instal':297C,300C 'interrupt':10A,34B,135C 'irq':57B,122C,130C,177C,253C,266C,271C,277C,283C 'irqf':182C 'kernel':2A,21B,66B,85C,216C 'leav':363C 'line':189C 'linux':1A,20B,29B,84C,240C 'linux-kernel':19B 'lr':250C 'may':136C 'name':239C 'narrow':320C 'none':237C 'notif':9A,36B,46B,99C,106C,121C,153C,309C,323C 'notifi':202C,301C 'null':61B,208C,217C,332C 'order':292C 'p':263C 'panic':6A,64B,212C 'path':103C,119C,288C,362C 'pc':245C 'pend':139C 'percpu':273C 'pid':228C 'point':348C 'pointer':62B,218C,366C 'preempt':236C 'probe':102C,141C,168C,360C 'problem':293C 'regist':32B,98C,104C,131C,338C 'registr':357C 'request':129C,180C 'resolv':91C 'restor':24B,53B,155C,175C 'run':355C 'safe':353C 'servic':74B 'set':39B,94C 'share':56B,183C,187C 'snapshot':23B,52B,160C,174C 'snapshot-restor':22B 'soon':126C 'sourc':68B 'state':342C 'still':207C 'still-nul':206C 'swapper/0':231C 'taint':233C 'taken':163C 'time':142C 'trace':258C 'trigger':191C 'two':327C 'uid':226C 'unabl':213C 'unbind':376C 'virt':92C,243C 'virtual':221C 'vm':26B 'vm-guest':25B 'vmgenid':3A,30B,93C,201C,251C,264C 'vmgenid_notify.isra':246C,259C 'vmm':147C 'vulner':88C 'window':318C 'workqueu':315C 'x14/0x34':256C,269C 'x24/0x8c':249C,262C 'x44/0x1bc':275C 'x4c/0xb4':280C 'xf8/0x1f8':285C","nicknames":[],"mitigations":[],"who_affected":"The bug is in the vmgenid virtual machine generation ID driver, which runs on guests that expose a VM generation ID device, such as Firecracker microVMs using snapshot restore, via devicetree or ACPI. Hosts and guests without this device or driver are not exposed. The sources do not state which kernel versions are vulnerable.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:38+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98841","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98841","severity":null,"published_at":"2026-10-18T16:17:38+00:00","modified_at":"2026-10-19T10:19:48+00:00","first_seen_at":"2026-10-23T21:57:17+00:00","fetched_at":"2026-10-23T22:28:56+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}