{"id":"CVE-2026-99123","kind":"vulnerability","aliases":["CVE-2026-99123"],"related":[],"title":"Linux kernel: virtio vsock accepts packets from unrelated sources","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nvsock/virtio: validate packet source for connected sockets\n\nvirtio_transport_recv_pkt() looks up sockets first by the full source and\ndestination tuple, then by destination only in the bound table. The\nfallback is needed for listening and connecting sockets, but sockets remain\nin the bound table after connect(), so it can also return a non-listening\nsocket.\n\nThe fallback does not validate the source address. In TCP_SYN_SENT, a\nRESPONSE from an unrelated source can transition the victim socket to\nTCP_ESTABLISHED while its stored remote address remains unchanged.\nSubsequent RW packets from that source are delivered through the same\ndestination-only fallback.\n\nThis was reproduced with capability-empty processes under different UIDs.\nThe attacker discovered the target tuple through unprivileged AF_VSOCK\nsock_diag and caused the victim socket to read 16 attacker-chosen bytes;\nthe intended peer-side socket read 0 of those 16 bytes.\n\nAdd vsock_check_source() to validate the transport, source port and source\nCID against the peer stored in a non-listening socket. The local transport\nis the CID exception because its packets are generated internally with\nVMADDR_CID_LOCAL as their source, including connections using CID aliases.\n\nUse the helper after lock_sock() in the virtio receive path.","summary":"A connected AF_VSOCK socket in the Linux kernel can be moved to an established state by a packet from an unrelated source, because the virtio receive path falls back to destination-only socket lookup without checking the source. A local unprivileged process can then inject data into the victim socket, which reads attacker-chosen bytes.","severity":"high","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["linux-kernel","runtime","virtio","virtualization","vsock"],"not_affected_if":["no-untrusted-local-users","no-virtio-vsock"],"how_to_check":"- `uname -r` and compare against the fixed kernel version listed by your distribution's advisory for CVE-2026-99123\n- `lsmod | grep -E 'vmw_vsock_virtio_transport|vhost_vsock'` to see whether virtio vsock is loaded at all\n- unknown whether the sources list a specific affected version range","fix":"- Update the Linux kernel to a release that includes the vsock_check_source() fix, per your distribution's kernel update\n- If vsock is not needed, unload or blacklist `virtio_vsock` and `vhost_vsock` until patched (unknown whether this fully mitigates on every configuration)","status":"open","published_at":"2026-10-28T11:17:31+00:00","first_seen_at":"2026-10-28T11:32:34+00:00","triaged_at":"2026-10-28T11:37:30+00:00","updated_at":"2026-10-28T11:37:30+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-10-28T11:37:30Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release that includes the vsock_check_source() fix, per your distribution's kernel update\n- If vsock is not needed, unload or blacklist `virtio_vsock` and `vhost_vsock` until patched (unknown whether this fully mitigates on every configuration)","reach":"local","title":"Linux kernel: virtio vsock accepts packets from unrelated sources","impact":"medium","summary":"A connected AF_VSOCK socket in the Linux kernel can be moved to an established state by a packet from an unrelated source, because the virtio receive path falls back to destination-only socket lookup without checking the source. A local unprivileged process can then inject data into the victim socket, which reads attacker-chosen bytes.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","virtualization","vsock","virtio"],"confidence":0.6,"needs_auth":"no","worst_case":"unprivileged local user injects data into a connected kernel socket","analyst_note":"Find the fixed kernel versions and stable backport commits for CVE-2026-99123 in the NVD entry and the upstream kernel git log for vsock_check_source().","how_to_check":"- `uname -r` and compare against the fixed kernel version listed by your distribution's advisory for CVE-2026-99123\n- `lsmod | grep -E 'vmw_vsock_virtio_transport|vhost_vsock'` to see whether virtio vsock is loaded at all\n- unknown whether the sources list a specific affected version range","needs_analyst":true,"not_affected_if":["no-virtio-vsock","no-untrusted-local-users"],"who_is_affected":"Systems running a Linux kernel with virtio vsock support, such as virtual machines and hypervisor hosts that use AF_VSOCK for host-guest communication. Exposure depends on local unprivileged users being able to create AF_VSOCK sockets on the machine. Hosts without virtio vsock loaded are unlikely to be affected; the sources do not say more.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000733,"input_tokens":3666,"output_tokens":733,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':11A,14A '-99123':12A,15A '0':239C '16':227C,242C 'accept':5A 'add':244C 'address':156C,179C 'af':25B,216C 'alias':291C 'also':142C 'attack':78B,209C,229C 'attacker-chosen':77B,228C 'back':52B 'bound':119C,135C 'byte':80B,231C,243C 'capability-empti':201C 'capabl':202C 'caus':221C 'check':60B,246C 'chosen':79B,230C 'cid':256C,272C,282C,290C 'connect':24B,96C,128C,138C,288C 'cve':10A,13A 'data':70B 'deliv':189C 'destin':55B,111C,115C,194C 'destination-on':54B,193C 'diag':219C 'differ':206C 'discov':210C 'empti':203C 'establish':37B,174C 'except':273C 'fall':51B 'fallback':122C,150C,196C 'first':105C 'follow':86C 'full':108C 'generat':278C 'helper':294C 'includ':287C 'inject':69B 'intend':233C 'intern':279C 'kernel':2A,18B,31B,84C 'linux':1A,17B,30B,83C 'linux-kernel':16B 'listen':126C,147C,265C 'local':64B,268C,283C 'lock':296C 'look':102C 'lookup':58B 'move':34B 'need':124C 'non':146C,264C 'non-listen':145C,263C 'packet':6A,41B,93C,184C,276C 'path':50B,302C 'peer':235C,259C 'peer-sid':234C 'pkt':101C 'port':253C 'process':66B,204C 'read':76B,226C,238C 'receiv':49B,301C 'recv':100C 'remain':132C,180C 'remot':178C 'reproduc':199C 'resolv':90C 'respons':162C 'return':143C 'runtim':19B 'rw':183C 'sent':160C 'side':236C 'sock':218C,297C 'socket':27B,57B,74B,97C,104C,129C,131C,148C,171C,224C,237C,266C 'sourc':9A,45B,62B,94C,109C,155C,166C,187C,247C,252C,255C,286C 'state':38B 'store':177C,260C 'subsequ':182C 'syn':159C 'tabl':120C,136C 'target':212C 'tcp':158C,173C 'transit':168C 'transport':99C,251C,269C 'tupl':112C,213C 'uid':207C 'unchang':181C 'unprivileg':65B,215C 'unrel':8A,44B,165C 'use':289C,292C 'valid':92C,153C,249C 'victim':73B,170C,223C 'virtio':3A,20B,48B,98C,300C 'virtual':21B 'vmaddr':281C 'vsock':4A,22B,26B,217C,245C 'vsock/virtio':91C 'vulner':87C 'without':59B","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel with virtio vsock support, such as virtual machines and hypervisor hosts that use AF_VSOCK for host-guest communication. Exposure depends on local unprivileged users being able to create AF_VSOCK sockets on the machine. Hosts without virtio vsock loaded are unlikely to be affected; the sources do not say more.","tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-28T11:17:31+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99123","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99123","severity":null,"published_at":"2026-10-28T11:17:31+00:00","modified_at":"2026-10-28T11:17:31+00:00","first_seen_at":"2026-10-28T11:32:34+00:00","fetched_at":"2026-10-28T11:32:34+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"}