{"id":"CVE-2026-31531","state":"PUBLISHED","title":"ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()","description":"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 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","publishedAt":"2026-04-23T11:12:44.143Z","updatedAt":"2026-10-30T12:24:19.337Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"5f479aac1262959e54cdd978d873be5f202e2a40","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"18a4543c1750f96be63e349936d2dfdcb360b2dc","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"615517f3f8d53b0cf41507c7599971e17adfdfa5","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"40bd39e383a0478fd5c221f393df05fd9d70cfbc","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"635038fe19db391117e66b46bdc2b6e447ac801d","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"14cf0cd35361f4e94824bf8a42f72713d7702a73","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/nexthop.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.3","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.83","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.24","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.14","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/nexthop.c"]}],"references":["https://git.kernel.org/stable/c/5f479aac1262959e54cdd978d873be5f202e2a40","https://git.kernel.org/stable/c/18a4543c1750f96be63e349936d2dfdcb360b2dc","https://git.kernel.org/stable/c/615517f3f8d53b0cf41507c7599971e17adfdfa5","https://git.kernel.org/stable/c/40bd39e383a0478fd5c221f393df05fd9d70cfbc","https://git.kernel.org/stable/c/635038fe19db391117e66b46bdc2b6e447ac801d","https://git.kernel.org/stable/c/14cf0cd35361f4e94824bf8a42f72713d7702a73"],"weaknesses":[],"ingestedAt":"2026-10-30T12:42:04.495Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31531.json","commit":"db8103c5921aac81d5d90efcf3745980dafabf49","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31531","state":"PUBLISHED","datePublished":"2026-04-23T11:12:44.143Z","dateUpdated":"2026-10-30T12:24:19.337Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.112Z"},"containers":{"cna":{"title":"ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()","descriptions":[{"lang":"en","value":"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 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"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"5f479aac1262959e54cdd978d873be5f202e2a40","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"18a4543c1750f96be63e349936d2dfdcb360b2dc","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"615517f3f8d53b0cf41507c7599971e17adfdfa5","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"40bd39e383a0478fd5c221f393df05fd9d70cfbc","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"635038fe19db391117e66b46bdc2b6e447ac801d","versionType":"git"},{"version":"430a049190de3c9e219f43084de9f1122da04570","status":"affected","lessThan":"14cf0cd35361f4e94824bf8a42f72713d7702a73","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/nexthop.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.3","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.83","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.24","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.14","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/nexthop.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/5f479aac1262959e54cdd978d873be5f202e2a40"},{"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"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:24:19.337Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.12.83"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.18.24"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.19.14"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"7.0"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}