{"id":"CVE-2026-80725","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-80725","summary":"net: gro: properly validate BIG TCP aggregation criteria","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: gro: properly validate BIG TCP aggregation criteria\n\nWhen GRO attempts to aggregate packets beyond GRO_LEGACY_MAX_SIZE (64KB),\nBIG TCP should only be permitted for plain IPv4 TCP and plain IPv6 TCP\n(with sufficient MAC header room to insert the temporary HBH jumbo header).\n\nHowever, commit b1a78b9b9886 (\"net: add support for ipv4 big tcp\")\nloosened the check in skb_gro_receive(), leading to several issues:\n\n1. skb_gro_receive() checked skb_headroom(p) instead of the actual space\n   before the MAC header (p->mac_header). Because skb_headroom(p) includes\n   mac_len, crafted frames (e.g. injected via AF_PACKET) can pass the check\n   with p->mac_header < 8 bytes. When ipv6_gro_complete() inserts the\n   temporary HBH jumbo header, the memmove() starts before skb->head,\n   causing an out-of-bounds write and wrapping skb->mac_header.\n2. It allowed non-IP protocols such as software VLAN (ETH_P_8021Q /\n   ETH_P_8021AD) to aggregate beyond 64KB because\n   p->protocol != ETH_P_IPV6 was true.\n3. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark,\n   allowing encapsulated flows (e.g. SIT / IPv6-in-IPv4) to aggregate\n   beyond 64KB.\n\nFix skb_gro_receive() to strictly enforce:\n- NAPI_GRO_CB(skb)->proto == IPPROTO_TCP\n- Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation)\n- Protocol must be either ETH_P_IP or ETH_P_IPV6\n- If ETH_P_IPV6, p->mac_header must be at least\n  sizeof(struct hop_jumbo_hdr)\n\nReturning -E2BIG from skb_gro_receive() ensures that packets which cannot\nbecome BIG TCP are cleanly flushed at <= 64KB and delivered intact without\ndropping.\n\nThis issue does not exist in mainline (7.0+) because the subsystem was\nrewritten in commit 81be30c1f5f2 (\"net/ipv6: Drop HBH for BIG TCP on RX\nside\"), making this fix relevant only for older stable branches like\n6.18.y.","published":"2026-08-29T06:39:35.212Z","modified":"2026-09-05T03:48:20.099713651Z","cvss":{"score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.1.185"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/03cb8cc2961f5f781d12e903782cb3815ed84b1c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/37a5dcd6837fc2afc44a7bc3ed8af4e983783d46"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3ce832e2bd431d0c12ba525ed73ad8fbc4191da5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/81be30c1f5f2bffda1f04c0efd0746af10b9643a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e907bf694ed55bdfe421be99dba35751a655df25"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80725.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80725"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-05T03:48:20.099713651Z"}}