{"id":"AZL-110762","summary":"CVE-2026-98954 affecting package kernel 6.6.157.1-1","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: always dissect GSO packets in __virtio_net_hdr_to_skb()\n\nCommit 9e8db5913264 (\"net: avoid false positives in untrusted gso\nvalidation\") added a '&& skb-\u003enetwork_header' check before flow-dissecting\nGSO packets without VIRTIO_NET_HDR_F_NEEDS_CSUM in\n__virtio_net_hdr_to_skb(), because some callers (such as tun_get_user(),\ntun_xdp_one(), virtnet_receive_done(), and raw_verify_header()) called\nvirtio_net_hdr_*_to_skb() before initializing skb-\u003enetwork_header and\nskb-\u003edev.\n\nBecause __alloc_skb() and __build_skb_around() zero-initialize\nskb-\u003enetwork_header to 0 (unlike mac_header and transport_header which\nare initialized to ~0U), those four callers always had\nskb-\u003enetwork_header == 0 and bypassed flow dissection in\n__virtio_net_hdr_to_skb(). More generally, skb-\u003enetwork_header is an\noffset from skb-\u003ehead (where 0 is also a valid offset whenever\nskb_headroom(skb) is 0), not a boolean flag.\n\nWhenever the 'if (gso_type && skb-\u003enetwork_header)' branch was skipped,\nthe fallback 'else if (gso_type)' only pulled nh_min_len + thlen (40 bytes\nfor TCPv4) without dissecting the packet, without validating ip_proto or\nn_proto, and without setting skb-\u003etransport_header.\n\nIf the packet has a malformed network header, it is not rejected and a\nsubsequent skb_probe_transport_header() also fails, leaving\nskb-\u003etransport_header at ~0U (0xffff). Similarly, if an IPv4 packet\ncarries IP options (ihl \u003e 5) or an IPv6 packet carries extension headers,\npulling only nh_min_len + thlen can leave the TCP header outside\nskb-\u003ehead. In both cases, tcp_hdrlen(skb) in skb_gso_transport_seglen()\nreads out-of-bounds:\n\n  BUG: KASAN: slab-out-of-bounds in skb_gso_transport_seglen\n  Read of size 2 by task poc/133\n  skb_gso_transport_seglen (net/core/gso.c:155)\n  skb_gso_validate_mac_len (net/core/gso.c:270)\n  tbf_enqueue (net/sched/sch_tbf.c:260)\n  dev_qdisc_enqueue (net/core/dev.c:4227)\n  __dev_queue_xmit (net/core/dev.c:4884)\n\nIn addition, checking virtio_net_hdr_match_proto() only inside\n'if (!skb-\u003eprotocol)' before flow dissection both skipped validation when\nskb-\u003eprotocol was pre-set by the caller and rejected VLAN-tagged frames\nwhose outer L2 protocol is ETH_P_8021Q or ETH_P_8021AD.\n\nFix this by:\n1. Initializing skb-\u003edev and skb-\u003enetwork_header (plus skb-\u003eprotocol for\n   IFF_TUN) before virtio_net_hdr_*_to_skb() in tun_get_user(),\n   tun_xdp_one(), virtnet_receive_done(), and raw_verify_header(). In\n   tun_get_user(), drop the redundant skb_reset_mac_header(skb) in the\n   IFF_TUN case since __virtio_net_hdr_to_skb() unconditionally resets\n   mac_header.\n2. Removing '&& skb-\u003enetwork_header' and the unvalidated\n   'else if (gso_type)' fallback in __virtio_net_hdr_to_skb() so all GSO\n   packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are flow-dissected, have\n   their transport header pulled into linear data, and have\n   skb-\u003etransport_header set.\n3. Moving the virtio_net_hdr_match_proto() check to after\n   skb_flow_dissect_flow_keys_basic(), validating keys.basic.n_proto\n   against hdr_gso_type.","modified":"2026-10-25T05:30:37Z","published":"2026-10-23T13:17:16Z","upstream":["CVE-2026-98954"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98954"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.157.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-110762.json"}}],"schema_version":"1.9.0"}