{"id":"CVE-2026-98800","kind":"vulnerability","aliases":["CVE-2026-98800"],"related":[],"title":"Linux kernel: BPF trampoline prog freed too early, enabling use-after-free","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Wait for an RCU tasks grace period before freeing trampoline progs\n\nWhen a prog is detached from a trampoline, it is freed after an RCU\ngrace period, or an RCU tasks trace one if it is sleepable. This covers\nthe tasks that are running the prog, since the prog's enter helper takes\nthe matching read lock before the prog is called. On a preemptible\nkernel, it doesn't cover a task that was preempted in the trampoline\njust before the enter helper. That task holds no lock yet, and it calls\nthe prog after it was freed:\n\n  BUG: KASAN: vmalloc-out-of-bounds in __bpf_prog_enter_recur+0x3a5/0x3f0\n  Read of size 8 at addr ffffc90000055040 by task candidate/110\n  CPU: 1 UID: 0 PID: 110 Comm: candidate Not tainted 7.3.0-rc2-00014-g15071f2a1263-dirty #2 PREEMPT(full)\n  Call Trace:\n   <TASK>\n   __bpf_prog_enter_recur+0x3a5/0x3f0\n   bpf_trampoline_6442509193+0x37/0xf1\n   __x64_sys_futex+0x9/0x410\n   do_syscall_64+0xb0/0x530\n   ...\n\nWait for an RCU tasks grace period before the existing one when freeing\na prog that was linked to a trampoline. An RCU tasks grace period only\nends once the tasks that were preempted have run again, and\nbpf_tramp_image_put() already relies on it to free the image. It doesn't\nwait for tasks that sleep in the trampoline, the next commit takes care\nof those.\n\nOnly progs that were linked to a trampoline can be called this way, so\nbpf_trampoline_add_prog() marks them and other progs are still freed as\nbefore.","summary":"When a BPF program is detached from a trampoline on a preemptible kernel, it can be freed while a preempted task still calls it, causing a KASAN-detected out-of-bounds read. The sources describe a kernel memory-safety bug that can crash the system or read freed memory.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["bpf","linux-kernel","preemptible-kernel","runtime"],"not_affected_if":["default-config"],"how_to_check":null,"fix":null,"status":"open","published_at":"2026-10-18T16:17:34+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","triaged_at":"2026-10-25T05:15:06+00:00","updated_at":"2026-10-25T05:15:06+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-25T05:15:06Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"local","title":"Linux kernel: BPF trampoline prog freed too early, enabling use-after-free","impact":"medium","summary":"When a BPF program is detached from a trampoline on a preemptible kernel, it can be freed while a preempted task still calls it, causing a KASAN-detected out-of-bounds read. The sources describe a kernel memory-safety bug that can crash the system or read freed memory.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","bpf","preemptible-kernel"],"confidence":0.5,"needs_auth":"unknown","worst_case":"kernel memory is read after free, causing crash or possible data disclosure","analyst_note":"Find the affected and fixed kernel versions and the upstream fix commit from the NVD entry at https://nvd.nist.gov/vuln/detail/CVE-2026-98800 and the linked kernel.org commit.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["default-config"],"who_is_affected":"Systems running a Linux kernel with BPF trampolines on a preemptible kernel build, where BPF programs are attached and detached at runtime; the sources do not name affected version ranges. Systems without BPF trampoline use are unlikely to be exposed, but the sources do not confirm this.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000635,"input_tokens":3850,"output_tokens":500,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'+0':201C,238C,243C,248C,253C '-00014':225C '-2026':15A,18A '-98800':16A,19A '0':216C '1':214C '110':218C '2':229C '64':252C '6442509193':242C '7.3.0':223C '8':206C 'add':339C 'addr':208C 'alreadi':297C 'bound':60B,195C 'bpf':3A,20B,30B,90C,197C,234C,240C,293C,337C 'bug':70B,189C 'call':50B,152C,182C,232C,333C 'candid':220C 'candidate/110':212C 'care':320C 'caus':52B 'comm':219C 'commit':318C 'cover':129C,160C 'cpu':213C 'crash':73B 'cve':14A,17A 'describ':64B 'detach':33B,106C 'detect':56B 'dirti':228C 'doesn':158C,306C 'earli':8A 'enabl':9A 'end':282C 'enter':141C,172C,199C,236C 'exist':264C 'ffffc90000055040':209C 'follow':85C 'free':13A,99C,267C,302C 'freed':6A,44B,78B,112C,188C,348C 'full':231C 'futex':247C 'g15071f2a1263':227C 'g15071f2a1263-dirty':226C 'grace':96C,116C,260C,279C 'helper':142C,173C 'hold':176C 'imag':295C,304C 'kasan':55B,190C 'kasan-detect':54B 'kernel':2A,23B,26B,40B,66B,83C,156C 'link':272C,327C 'linux':1A,22B,82C 'linux-kernel':21B 'lock':147C,178C 'mark':341C 'match':145C 'memori':68B,79B 'memory-safeti':67B 'next':317C 'one':123C,265C 'out-of-bound':57B 'period':97C,117C,261C,280C 'pid':217C 'preempt':47B,165C,230C,288C 'preemptibl':25B,39B,155C 'preemptible-kernel':24B 'prog':5A,101C,104C,136C,139C,150C,184C,198C,235C,269C,324C,340C,345C 'program':31B 'put':296C 'rc2':224C 'rcu':94C,115C,120C,258C,277C 'read':61B,77B,146C,203C 'recur':200C,237C 'reli':298C 'resolv':89C 'run':134C,290C 'runtim':27B 'safeti':69B 'sinc':137C 'size':205C 'sleep':312C 'sleepabl':127C 'sourc':63B 'still':49B,347C 'sys':246C 'syscal':251C 'system':75B 'taint':222C 'take':143C,319C 'task':48B,95C,121C,131C,162C,175C,211C,259C,278C,285C,310C 'trace':122C,233C 'tramp':294C 'trampolin':4A,36B,100C,109C,168C,241C,275C,315C,330C,338C 'uid':215C 'use':11A 'use-after-fre':10A 'vmalloc':192C 'vmalloc-out-of-bound':191C 'vulner':86C 'wait':91C,255C,308C 'way':335C 'x37/0xf1':244C 'x3a5/0x3f0':202C,239C 'x64':245C 'x9/0x410':249C 'xb0/0x530':254C 'yet':179C","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel with BPF trampolines on a preemptible kernel build, where BPF programs are attached and detached at runtime; the sources do not name affected version ranges. Systems without BPF trampoline use are unlikely to be exposed, but the sources do not confirm this.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:34+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98800","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98800","severity":null,"published_at":"2026-10-18T16:17:34+00:00","modified_at":"2026-10-19T10:19:44+00:00","first_seen_at":"2026-10-23T21:57:16+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"}