GHSA-MRF2-HC9C-229V

Vulnerability from github – Published: 2026-06-25 09:31 – Updated: 2026-06-28 09:31
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nft_ct: bail out on template ct in get eval

I noticed this issue while looking at a historic syzbot report 1.

A rule like the one below is enough to trigger the bug:

table ip t {
    chain pre {
        type filter hook prerouting priority raw;
        ct zone set 1
        ct original saddr 1.2.3.4 accept
    }
}

The first expression attaches a per-cpu template ct via nft_ct_set_zone_eval() (nf_ct_tmpl_alloc -> kzalloc, tuple is all zero, nf_ct_l3num(ct) == 0). The next expression then calls nft_ct_get_eval() on the same skb, treats the template as a real ct and hits the 16-byte memcpy path. With dreg at NFT_REG32_15 this overflows past struct nft_regs on the kernel stack; with smaller dreg values it silently clobbers adjacent registers.

Reject template ct at the eval entry and in nft_ct_get_fast_eval(), mirroring the check nft_ct_set_eval() already has. Additionally, bound the address copy in NFT_CT_SRC / NFT_CT_DST by priv->len instead of by nf_ct_l3num(ct): nf_ct_get_tuple() zeroes the tuple before pkt_to_tuple() fills in only the protocol-relevant leading bytes, so the trailing bytes of tuple->{src,dst}.u3.all are well-defined zero. priv->len is validated at rule load, so the copy size is now bounded by the destination register rather than by an untrusted field on the conntrack.

Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-53267"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-25T09:16:44Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nft_ct: bail out on template ct in get eval\n\nI noticed this issue while looking at a historic syzbot report [1].\n\nA rule like the one below is enough to trigger the bug:\n\n    table ip t {\n        chain pre {\n            type filter hook prerouting priority raw;\n            ct zone set 1\n            ct original saddr 1.2.3.4 accept\n        }\n    }\n\nThe first expression attaches a per-cpu template ct via\nnft_ct_set_zone_eval() (nf_ct_tmpl_alloc -\u003e kzalloc, tuple is all\nzero, nf_ct_l3num(ct) == 0). The next expression then calls\nnft_ct_get_eval() on the same skb, treats the template as a real ct\nand hits the 16-byte memcpy path. With dreg at NFT_REG32_15 this\noverflows past struct nft_regs on the kernel stack; with smaller\ndreg values it silently clobbers adjacent registers.\n\nReject template ct at the eval entry and in nft_ct_get_fast_eval(),\nmirroring the check nft_ct_set_eval() already has. Additionally,\nbound the address copy in NFT_CT_SRC / NFT_CT_DST by priv-\u003elen\ninstead of by nf_ct_l3num(ct): nf_ct_get_tuple() zeroes the tuple\nbefore pkt_to_tuple() fills in only the protocol-relevant leading\nbytes, so the trailing bytes of tuple-\u003e{src,dst}.u3.all are\nwell-defined zero. priv-\u003elen is validated at rule load, so the\ncopy size is now bounded by the destination register rather than\nby an untrusted field on the conntrack.\n\n[1]: https://syzkaller.appspot.com/bug?id=389cf09cb72926114fce90dc85a2c3231dcb647c",
  "id": "GHSA-mrf2-hc9c-229v",
  "modified": "2026-06-28T09:31:47Z",
  "published": "2026-06-25T09:31:23Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53267"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2e154b5f53f1b0b490c7b8b02499f90feb86b1d5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3027ecbdb5fdf9200251c21d4818e4c447ef78e1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8470f676eadeab99132708acb1a85915664d6115"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/af80f78ce984649e1698b841cd33f4fa505ad828"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f071b0bf078146368d18e4eec386bf2ddc0ab7e0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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