{"id":"CVE-2026-80725","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-80725","generatedAt":"2026-10-28T02:22:59.246Z","title":"In the Linux kernel, the following vulnerability has been resolved: net: gro: properly validate BIG TCP aggregation criteria When GRO attempts to aggregate packets beyond GRO_LEGACY_MAX_SIZE (64KB), BIG TCP should only be permitted for plain IPv4 TCP…","description":"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":"2026-08-29T07:16:55.000Z","lastModified":"2026-10-16T20:18:09.000Z","status":"Received","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","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"},"cwe":[],"affected":[],"epss":{"score":0.00459,"percentile":0.39527,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.46%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/03cb8cc2961f5f781d12e903782cb3815ed84b1c","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/37a5dcd6837fc2afc44a7bc3ed8af4e983783d46","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/3ce832e2bd431d0c12ba525ed73ad8fbc4191da5","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/81be30c1f5f2bffda1f04c0efd0746af10b9643a","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e907bf694ed55bdfe421be99dba35751a655df25","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-80725","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}