GHSA-4JWG-G8H6-9GV7
Vulnerability from github – Published: 2026-10-23 15:31 – Updated: 2026-10-23 15:31In the Linux kernel, the following vulnerability has been resolved:
flow_dissector: avoid u16 truncation of hlen in bpf_flow_dissect()
bpf_flow_dissect() sanitizes the offsets returned by the BPF program with clamp_t(u16, ..., hlen).
If hlen is bigger than 65535, the upper bound is truncated before the comparison. For instance, with hlen == 65536, both nhoff and thoff are forced to zero, even if the program returned sane values.
This is the same class of bug as the one fixed in commit 99bda1ecbd56 ("flow_dissector: avoid u16 truncation of skb->len when computing thoff"). That fix does not cover the BPF path, because __skb_flow_dissect() returns early when a BPF flow dissector handles the packet.
struct bpf_flow_keys stores nhoff and thoff as u16, so cap hlen to U16_MAX before clamping.
Found by sashiko while reviewing the commit above.
{
"affected": [],
"aliases": [
"CVE-2026-98950"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-10-23T13:17:16Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nflow_dissector: avoid u16 truncation of hlen in bpf_flow_dissect()\n\nbpf_flow_dissect() sanitizes the offsets returned by the BPF program\nwith clamp_t(u16, ..., hlen).\n\nIf hlen is bigger than 65535, the upper bound is truncated before\nthe comparison. For instance, with hlen == 65536, both nhoff and\nthoff are forced to zero, even if the program returned sane values.\n\nThis is the same class of bug as the one fixed in commit 99bda1ecbd56\n(\"flow_dissector: avoid u16 truncation of skb-\u003elen when computing\nthoff\"). That fix does not cover the BPF path, because\n__skb_flow_dissect() returns early when a BPF flow dissector\nhandles the packet.\n\nstruct bpf_flow_keys stores nhoff and thoff as u16, so cap hlen\nto U16_MAX before clamping.\n\nFound by sashiko while reviewing the commit above.",
"id": "GHSA-4jwg-g8h6-9gv7",
"modified": "2026-10-23T15:31:32Z",
"published": "2026-10-23T15:31:32Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98950"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3fb5ad2951a6df92c98f4f06cd70f20c50a2eb2a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/61b43a51a55929ec040bee3ea51af2121b956d05"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c44c02c930c6583b235a1937c69ff716c4bb4514"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cc18eb0e9941162c03f03f411ed7f6c339d91fa0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f202578efc738b883cfa04889eb97328914265a7"
}
],
"schema_version": "1.4.0",
"severity": []
}
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