{"id":"CVE-2026-98829","kind":"vulnerability","aliases":["CVE-2026-98829"],"related":[],"title":"Linux kernel: oversized Wi-Fi fragments overflow a counter and crash the kernel","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nwifi: mac80211: drop oversized fragments to avoid extra_len overflow\n\nIn ieee80211_rx_h_defragment(), fragment payloads are accumulated into\nentry->extra_len as subsequent fragments arrive:\n\n        entry->extra_len += rx->skb->len;\n\nWhen the final fragment arrives, the head fragment is dequeued, and\npskb_expand_head() is called with entry->extra_len to ensure sufficient\ntailroom for all queued fragments before copying:\n\n        if (skb_tailroom(rx->skb) < entry->extra_len) {\n                if (unlikely(pskb_expand_head(rx->skb, 0, entry->extra_len,\n                                              GFP_ATOMIC))) {\n                        ...\n                }\n        }\n        while ((skb = __skb_dequeue(&entry->skb_list))) {\n                skb_put_data(rx->skb, skb->data, skb->len);\n                dev_kfree_skb(skb);\n        }\n\nIn commit 69f132236827 (\"mac80211: shrink struct\nieee80211_fragment_entry\"), entry->extra_len was narrowed from unsigned\nint to u16 in order to reduce structure memory footprint.\n\nHowever, an IEEE 802.11 frame sequence can contain up to 16 fragments\n(frag numbers 0..15). If a sequence of large fragments arrives (e.g. from\na malicious peer or rogue AP), the sum of fragment lengths can exceed\n65535 bytes (for example, 15 fragments of 4400 bytes total 66000 bytes).\nBecause extra_len is a u16, this addition overflows and wraps around\nmodulo 65536 (e.g. 66000 wraps to 464).\n\nConsequently, pskb_expand_head() allocates only the truncated amount of\ntailroom (or is skipped entirely if the head fragment already has >= 464\nbytes of tailroom). When skb_put_data() subsequently iterates through the\nqueued skb list, it appends the full payload into the undersized buffer,\ncausing skb_put() to trigger skb_over_panic() and crash the kernel in\nsoftirq context.\n\nA legitimate MSDU in IEEE 802.11 is at most 2304 bytes (or up to 7935/11454\nbytes for A-MSDU, which is not fragmented), well below U16_MAX.\n\nFix this without increasing the size of struct ieee80211_fragment_entry by\nchecking whether adding the incoming fragment length would exceed U16_MAX.\nIf so, purge the queued fragments and drop the frame.\n\n[assign a separate drop reason]","summary":"A u16 length counter in the mac80211 Wi-Fi defragmentation path wraps when a sequence of large fragments sums past 65535 bytes, so the kernel allocates too little buffer and then panics in softirq context. A malicious peer or rogue access point can trigger this with crafted fragmented frames, causing a kernel crash.","severity":"high","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["embedded","kernel","linux","mac80211","runtime","wifi"],"not_affected_if":["no-wifi-hardware","wired-only"],"how_to_check":"- Run `uname -r` and compare against the kernel version that carries the upstream fix; the sources do not list fixed versions.\n- Check whether the machine uses Wi-Fi with mac80211-based drivers: `lsmod | grep mac80211`.\n- unknown","fix":"- Update the Linux kernel to a release that includes the upstream commit adding the U16_MAX check in ieee80211_rx_h_defragment (the sources do not name the version).\n- unknown","status":"open","published_at":"2026-10-18T16:17:37+00:00","first_seen_at":"2026-10-23T21:57:17+00:00","triaged_at":"2026-10-25T05:13:22+00:00","updated_at":"2026-10-25T05:13:22+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-10-25T05:13:22Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release that includes the upstream commit adding the U16_MAX check in ieee80211_rx_h_defragment (the sources do not name the version).\n- unknown","reach":"network","title":"Linux kernel: oversized Wi-Fi fragments overflow a counter and crash the kernel","impact":"medium","summary":"A u16 length counter in the mac80211 Wi-Fi defragmentation path wraps when a sequence of large fragments sums past 65535 bytes, so the kernel allocates too little buffer and then panics in softirq context. A malicious peer or rogue access point can trigger this with crafted fragmented frames, causing a kernel crash.","category":"runtime","nicknames":[],"who_cares":["linux","kernel","wifi","mac80211","embedded"],"confidence":0.6,"needs_auth":"no","worst_case":"Remote peer crashes the kernel through crafted Wi-Fi fragments.","analyst_note":"Check the NVD entry and the upstream kernel commit for the fixed stable versions and whether the default config is affected.","how_to_check":"- Run `uname -r` and compare against the kernel version that carries the upstream fix; the sources do not list fixed versions.\n- Check whether the machine uses Wi-Fi with mac80211-based drivers: `lsmod | grep mac80211`.\n- unknown","needs_analyst":true,"not_affected_if":["no-wifi-hardware","wired-only"],"who_is_affected":"Only systems that receive 802.11 traffic through the mac80211 stack are exposed, which means Linux machines with Wi-Fi interfaces that use mac80211 drivers, including laptops, Wi-Fi routers and embedded devices running Linux. Wired-only servers and containers without a Wi-Fi radio are not reached by this path. unknown whether fragmentation handling is enabled by default in all configurations.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000755,"input_tokens":4094,"output_tokens":691,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':16A,19A '-98829':17A,20A '0':169C,235C '15':236C,263C '16':231C '2304':359C '4400':266C '464':289C,311C '65535':48B,259C '65536':284C '66000':269C,286C '69f132236827':197C '7935/11454':364C '802.11':224C,355C 'a-msdu':367C 'access':68B 'accumul':109C 'add':392C 'addit':278C 'alloc':53B,294C 'alreadi':309C 'amount':298C 'ap':251C 'append':327C 'around':282C 'arriv':117C,128C,243C 'assign':411C 'atom':174C 'avoid':97C 'buffer':56B,334C 'byte':49B,260C,267C,270C,312C,360C,365C 'call':139C 'caus':77B,335C 'check':390C 'commit':196C 'consequ':290C 'contain':228C 'context':62B,349C 'copi':153C 'counter':10A,30B 'craft':74B 'crash':12A,80B,344C 'cve':15A,18A 'data':184C,188C,318C 'defrag':105C 'defragment':37B 'dequeu':133C,178C 'dev':191C 'drop':93C,408C,414C 'e.g':244C,285C 'embed':21B 'ensur':145C 'entir':304C 'entri':111C,118C,141C,159C,170C,179C,203C,204C,388C 'exampl':262C 'exceed':258C,398C 'expand':136C,165C,292C 'extra':98C,112C,119C,142C,160C,171C,205C,272C 'fi':6A,36B 'final':126C 'fix':378C 'follow':86C 'footprint':220C 'frag':233C 'fragment':7A,45B,75B,95C,106C,116C,127C,131C,151C,202C,232C,242C,255C,264C,308C,373C,387C,395C,406C 'frame':76B,225C,410C 'full':329C 'gfp':173C 'h':104C 'head':130C,137C,166C,293C,307C 'howev':221C 'ieee':223C,354C 'ieee80211':102C,201C,386C 'incom':394C 'increas':381C 'int':211C 'iter':320C 'kernel':2A,14A,22B,52B,79B,84C,346C 'kfree':192C 'larg':44B,241C 'legitim':351C 'len':99C,113C,120C,123C,143C,161C,172C,190C,206C,273C 'length':29B,256C,396C 'linux':1A,23B,83C 'list':181C,325C 'littl':55B 'mac80211':24B,33B,92C,198C 'malici':64B,247C 'max':377C,400C 'memori':219C 'modulo':283C 'msdu':352C,369C 'narrow':208C 'number':234C 'order':215C 'overflow':8A,100C,279C 'overs':3A,94C 'panic':59B,342C 'past':47B 'path':38B 'payload':107C,330C 'peer':65B,248C 'point':69B 'pskb':135C,164C,291C 'purg':403C 'put':183C,317C,337C 'queu':150C,323C,405C 'reason':415C 'reduc':217C 'resolv':90C 'rogu':67B,250C 'runtim':25B 'rx':103C,121C,157C,167C,185C 'separ':413C 'sequenc':42B,226C,239C 'shrink':199C 'size':383C 'skb':122C,155C,158C,168C,176C,177C,180C,182C,186C,187C,189C,193C,194C,316C,324C,336C,340C 'skip':303C 'softirq':61B,348C 'struct':200C,385C 'structur':218C 'subsequ':115C,319C 'suffici':146C 'sum':46B,253C 'tailroom':147C,156C,300C,314C 'total':268C 'trigger':71B,339C 'truncat':297C 'u16':28B,213C,276C,376C,399C 'unders':333C 'unlik':163C 'unsign':210C 'vulner':87C 'well':374C 'whether':391C 'wi':5A,35B 'wi-fi':4A,34B 'wifi':26B,91C 'without':380C 'would':397C 'wrap':39B,281C,287C","nicknames":[],"mitigations":[],"who_affected":"Only systems that receive 802.11 traffic through the mac80211 stack are exposed, which means Linux machines with Wi-Fi interfaces that use mac80211 drivers, including laptops, Wi-Fi routers and embedded devices running Linux. Wired-only servers and containers without a Wi-Fi radio are not reached by this path. unknown whether fragmentation handling is enabled by default in all configurations.","tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:37+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98829","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98829","severity":null,"published_at":"2026-10-18T16:17:37+00:00","modified_at":"2026-10-19T10:19:46+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"}