{"id":"CVE-2026-98742","kind":"vulnerability","aliases":["CVE-2026-98742"],"related":[],"title":"Linux ALSA sequencer: racing compat port ioctls can free a subscriber twice","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: seq: Serialize compat port-info ioctls\n\nThe native sequencer ioctl path serializes handler calls with\nclient->ioctl_mutex, but the translated port-info compat path invokes the\nsame handlers through snd_seq_kernel_client_ctl() without taking that\nmutex.\n\nThis lets concurrent compat CREATE_PORT requests pass the port-count\ncheck before any request reaches the serialized insertion. The computed\ninteger port index can then exceed the address field range and wrap to an\nexisting index. Subsequent subscriber teardown can resolve the duplicate\naddress to the wrong port and access a freed subscriber.\n\nTake ioctl_mutex while dispatching converted port-info requests, matching\nthe native ioctl path. All translated port-info commands share this\nhelper, so their accesses to the client port state are serialized as\nwell.","summary":"Concurrent 32-bit compatibility port-info ioctl calls to the ALSA sequencer skip the client mutex, so port indexes can wrap onto existing ones. Later subscriber teardown then reaches a freed subscriber, which can corrupt kernel memory.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["alsa","kernel","linux","multi-user-hosts","runtime"],"not_affected_if":["snd-seq-not-loaded"],"how_to_check":"- `uname -r` to see the running kernel version, then compare it against the fixed kernel in the NVD entry\n- Check whether the ALSA sequencer is loaded with `lsmod | grep snd_seq`; if it is absent, the flaw is not reachable\n- unknown","fix":"- Update the Linux kernel to a release that includes the upstream commit 'ALSA: seq: Serialize compat port-info ioctls'\n- unknown","status":"open","published_at":"2026-10-18T16:17:27+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","triaged_at":"2026-10-25T05:17:03+00:00","updated_at":"2026-10-25T05:17:03+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-10-25T05:17:03Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release that includes the upstream commit 'ALSA: seq: Serialize compat port-info ioctls'\n- unknown","reach":"local","title":"Linux ALSA sequencer: racing compat port ioctls can free a subscriber twice","impact":"high","summary":"Concurrent 32-bit compatibility port-info ioctl calls to the ALSA sequencer skip the client mutex, so port indexes can wrap onto existing ones. Later subscriber teardown then reaches a freed subscriber, which can corrupt kernel memory.","category":"runtime","nicknames":[],"who_cares":["linux","kernel","alsa","multi-user-hosts"],"confidence":0.6,"needs_auth":"yes","worst_case":"local user corrupts kernel memory, possibly gaining root","analyst_note":"Find the fixed kernel versions and affected stable branches in the NVD entry and the upstream kernel commit.","how_to_check":"- `uname -r` to see the running kernel version, then compare it against the fixed kernel in the NVD entry\n- Check whether the ALSA sequencer is loaded with `lsmod | grep snd_seq`; if it is absent, the flaw is not reachable\n- unknown","needs_analyst":true,"not_affected_if":["snd-seq-not-loaded"],"who_is_affected":"Systems running a Linux kernel with ALSA sequencer support, where a local process can issue 32-bit compat ioctls against /dev/snd/seq. Hosts without the sequencer loaded, or machines that run only 64-bit userspace without compat callers, are less exposed. Sources do not name specific distributions or kernel versions.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000661,"input_tokens":3514,"output_tokens":620,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':14A,17A '-98742':15A,18A '32':28B 'access':168C,198C 'address':146C,162C 'alsa':2A,19B,38B,75C 'bit':29B 'call':35B,90C 'check':129C 'client':42B,92C,111C,201C 'command':192C 'compat':5A,30B,78C,101C,120C 'comput':138C 'concurr':27B,119C 'convert':177C 'corrupt':62B 'count':128C 'creat':121C 'ctl':112C 'cve':13A,16A 'dispatch':176C 'duplic':161C 'exceed':144C 'exist':50B,153C 'field':147C 'follow':70C 'free':9A 'freed':58B,170C 'handler':89C,106C 'helper':195C 'host':25B 'index':46B,141C,154C 'info':33B,81C,100C,180C,191C 'insert':136C 'integ':139C 'invok':103C 'ioctl':7A,34B,82C,86C,93C,173C,185C 'kernel':20B,63B,68C,110C 'later':52B 'let':118C 'linux':1A,21B,67C 'match':182C 'memori':64B 'multi':23B 'multi-user-host':22B 'mutex':43B,94C,116C,174C 'nativ':84C,184C 'one':51B 'onto':49B 'pass':124C 'path':87C,102C,186C 'port':6A,32B,45B,80C,99C,122C,127C,140C,166C,179C,190C,202C 'port-count':126C 'port-info':31B,79C,98C,178C,189C 'race':4A 'rang':148C 'reach':56B,133C 'request':123C,132C,181C 'resolv':74C,159C 'runtim':26B 'seq':76C,109C 'sequenc':3A,39B,85C 'serial':77C,88C,135C,205C 'share':193C 'skip':40B 'snd':108C 'state':203C 'subscrib':11A,53B,59B,156C,171C 'subsequ':155C 'take':114C,172C 'teardown':54B,157C 'translat':97C,188C 'twice':12A 'user':24B 'vulner':71C 'well':207C 'without':113C 'wrap':48B,150C 'wrong':165C","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel with ALSA sequencer support, where a local process can issue 32-bit compat ioctls against /dev/snd/seq. Hosts without the sequencer loaded, or machines that run only 64-bit userspace without compat callers, are less exposed. Sources do not name specific distributions or kernel versions.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:27+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98742","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98742","severity":null,"published_at":"2026-10-18T16:17:27+00:00","modified_at":"2026-10-21T13:21:41+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"}