CVE-2026-31531 (GCVE-0-2026-31531)

Vulnerability from cvelistv5 – Published: 2026-04-23 11:12 – Updated: 2026-04-23 11:12
VLAI?
Title
ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()
Summary
In the Linux kernel, the following vulnerability has been resolved: ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop() When querying a nexthop object via RTM_GETNEXTHOP, the kernel currently allocates a fixed-size skb using NLMSG_GOODSIZE. While sufficient for single nexthops and small Equal-Cost Multi-Path groups, this fixed allocation fails for large nexthop groups like 512 nexthops. This results in the following warning splat: WARNING: net/ipv4/nexthop.c:3395 at rtm_get_nexthop+0x176/0x1c0, CPU#20: rep/4608 [...] RIP: 0010:rtm_get_nexthop (net/ipv4/nexthop.c:3395) [...] Call Trace: <TASK> rtnetlink_rcv_msg (net/core/rtnetlink.c:6989) netlink_rcv_skb (net/netlink/af_netlink.c:2550) netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344) netlink_sendmsg (net/netlink/af_netlink.c:1894) ____sys_sendmsg (net/socket.c:721 net/socket.c:736 net/socket.c:2585) ___sys_sendmsg (net/socket.c:2641) __sys_sendmsg (net/socket.c:2671) do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) </TASK> Fix this by allocating the size dynamically using nh_nlmsg_size() and using nlmsg_new(), this is consistent with nexthop_notify() behavior. In addition, adjust nh_nlmsg_size_grp() so it calculates the size needed based on flags passed. While at it, also add the size of NHA_FDB for nexthop group size calculation as it was missing too. This cannot be reproduced via iproute2 as the group size is currently limited and the command fails as follows: addattr_l ERROR: message exceeded bound of 1048
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 430a049190de3c9e219f43084de9f1122da04570 , < 615517f3f8d53b0cf41507c7599971e17adfdfa5 (git)
Affected: 430a049190de3c9e219f43084de9f1122da04570 , < 40bd39e383a0478fd5c221f393df05fd9d70cfbc (git)
Affected: 430a049190de3c9e219f43084de9f1122da04570 , < 635038fe19db391117e66b46bdc2b6e447ac801d (git)
Affected: 430a049190de3c9e219f43084de9f1122da04570 , < 14cf0cd35361f4e94824bf8a42f72713d7702a73 (git)
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    Linux Linux Affected: 5.3
Unaffected: 0 , < 5.3 (semver)
Unaffected: 6.12.83 , ≤ 6.12.* (semver)
Unaffected: 6.18.24 , ≤ 6.18.* (semver)
Unaffected: 6.19.14 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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          "product": "Linux",
          "programFiles": [
            "net/ipv4/nexthop.c"
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          "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  \u003cTASK\u003e\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  \u003c/TASK\u003e\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"
        }
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      "providerMetadata": {
        "dateUpdated": "2026-04-23T11:12:44.143Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/615517f3f8d53b0cf41507c7599971e17adfdfa5"
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          "url": "https://git.kernel.org/stable/c/40bd39e383a0478fd5c221f393df05fd9d70cfbc"
        },
        {
          "url": "https://git.kernel.org/stable/c/635038fe19db391117e66b46bdc2b6e447ac801d"
        },
        {
          "url": "https://git.kernel.org/stable/c/14cf0cd35361f4e94824bf8a42f72713d7702a73"
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      ],
      "title": "ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()",
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    "cveId": "CVE-2026-31531",
    "datePublished": "2026-04-23T11:12:44.143Z",
    "dateReserved": "2026-03-09T15:48:24.112Z",
    "dateUpdated": "2026-04-23T11:12:44.143Z",
    "state": "PUBLISHED"
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      "date": "2026-04-25",
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  }
}


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