{"id":"CVE-2026-31531","title":"ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()\n\nWhen querying a nexthop object via RTM_GETNEXTHOP, the kernel currently\nallocates a fixed-size skb using N…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 18a4543c1750f96be63e349936d2dfdcb360b2dc","Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 615517f3f8d53b0cf41507c7599971e17adfdfa5","Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 40bd39e383a0478fd5c221f393df05fd9d70cfbc","Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 635038fe19db391117e66b46bdc2b6e447ac801d","Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 14cf0cd35361f4e94824bf8a42f72713d7702a73","Linux 5.3"],"published":"2026-04-23","updated":"2026-10-21","sourceUpdated":"2026-10-21T12:39:26.586Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31531","references":[{"url":"https://git.kernel.org/stable/c/18a4543c1750f96be63e349936d2dfdcb360b2dc"},{"url":"https://git.kernel.org/stable/c/615517f3f8d53b0cf41507c7599971e17adfdfa5"},{"url":"https://git.kernel.org/stable/c/40bd39e383a0478fd5c221f393df05fd9d70cfbc"},{"url":"https://git.kernel.org/stable/c/635038fe19db391117e66b46bdc2b6e447ac801d"},{"url":"https://git.kernel.org/stable/c/14cf0cd35361f4e94824bf8a42f72713d7702a73"}],"tags":["cve.org"],"epss":0.00164,"epssPercentile":0.05299,"ingestedAt":"2026-10-21T12:48:53.664Z","slug":"CVE-2026-31531","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()\n\nWhen querying a nexthop object via RTM_GETNEXTHOP, the kernel currently\nallocates a fixed-size skb using NLMSG_GOODSIZE. While sufficient for\nsingle nexthops and small Equal-Cost Multi-Path groups, this fixed\nallocation fails for large nexthop groups like 512 nexthops.\n\nThis results in the following warning splat:\n\n WARNING: net/ipv4/nexthop.c:3395 at rtm_get_nexthop+0x176/0x1c0, CPU#20: rep/4608\n [...]\n RIP: 0010:rtm_get_nexthop (net/ipv4/nexthop.c:3395)\n [...]\n Call Trace:\n  <TASK>\n  rtnetlink_rcv_msg (net/core/rtnetlink.c:6989)\n  netlink_rcv_skb (net/netlink/af_netlink.c:2550)\n  netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344)\n  netlink_sendmsg (net/netlink/af_netlink.c:1894)\n  ____sys_sendmsg (net/socket.c:721 net/socket.c:736 net/socket.c:2585)\n  ___sys_sendmsg (net/socket.c:2641)\n  __sys_sendmsg (net/socket.c:2671)\n  do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)\n  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)\n  </TASK>\n\nFix this by allocating the size dynamically using nh_nlmsg_size() and\nusing nlmsg_new(), this is consistent with nexthop_notify() behavior. In\naddition, adjust nh_nlmsg_size_grp() so it calculates the size needed\nbased on flags passed. While at it, also add the size of NHA_FDB for\nnexthop group size calculation as it was missing too.\n\nThis cannot be reproduced via iproute2 as the group size is currently\nlimited and the command fails as follows:\n\naddattr_l ERROR: message exceeded bound of 1048\n\n## Affected\n\n- `Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 18a4543c1750f96be63e349936d2dfdcb360b2dc`\n- `Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 615517f3f8d53b0cf41507c7599971e17adfdfa5`\n- `Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 40bd39e383a0478fd5c221f393df05fd9d70cfbc`\n- `Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 635038fe19db391117e66b46bdc2b6e447ac801d`\n- `Linux >= 430a049190de3c9e219f43084de9f1122da04570 < 14cf0cd35361f4e94824bf8a42f72713d7702a73`\n- `Linux 5.3`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}