CVE-2026-31531 (GCVE-0-2026-31531)
Vulnerability from cvelistv5 – Published: 2026-04-23 11:12 – Updated: 2026-10-21 12:39
VLAI
EPSS
VEX
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
5.5 (Medium)
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
430a049190de3c9e219f43084de9f1122da04570 , < 18a4543c1750f96be63e349936d2dfdcb360b2dc
(git)
Affected: 430a049190de3c9e219f43084de9f1122da04570 , < 615517f3f8d53b0cf41507c7599971e17adfdfa5 (git) Affected: 430a049190de3c9e219f43084de9f1122da04570 , < 40bd39e383a0478fd5c221f393df05fd9d70cfbc (git) Affected: 430a049190de3c9e219f43084de9f1122da04570 , < 635038fe19db391117e66b46bdc2b6e447ac801d (git) Affected: 430a049190de3c9e219f43084de9f1122da04570 , < 14cf0cd35361f4e94824bf8a42f72713d7702a73 (git) |
guessed | |
| Linux | Linux |
Affected:
5.3
Unaffected: 0 , < 5.3 (semver) Unaffected: 6.6.160 , ≤ 6.6.* (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) |
guessed |
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}
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"url": "https://git.kernel.org/stable/c/14cf0cd35361f4e94824bf8a42f72713d7702a73"
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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"
}
],
"id": "CVE-2026-31531",
"lastModified": "2026-10-21T13:18:39.050",
"metrics": {
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{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 5.5,
"baseSeverity": "MEDIUM",
"confidentialityImpact": "NONE",
"integrityImpact": "NONE",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"version": "3.1"
},
"exploitabilityScore": 1.8,
"impactScore": 3.6,
"source": "nvd@nist.gov",
"type": "Primary"
}
]
},
"published": "2026-04-23T12:17:01.820",
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"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Modified",
"weaknesses": [
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"value": "NVD-CWE-noinfo"
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"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-06-28T07:26:11+00:00",
"cve": "CVE-2026-31531",
"id": "CVE-2026-31531",
"initial_release_date": "2026-04-23T00:00:00+00:00",
"product_status:known_affected": "184",
"product_status:known_not_affected": "90",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: ipv4: nexthop: allocate skb dynamically in rtm_get_nexthop()",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31531.json",
"version": "3"
}
}
}
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Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.