CVE-2026-53267 (GCVE-0-2026-53267)
Vulnerability from cvelistv5
Published
2026-06-25 08:39
Modified
2026-08-05 12:34
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
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. [1]: https://syzkaller.appspot.com/bug?id=389cf09cb72926114fce90dc85a2c3231dcb647c
References
Impacted products
Vendor Product Version
Linux Linux Version: 45d9bcda21f4c13be75e3571b0f0ef39e77934b5
Version: 45d9bcda21f4c13be75e3571b0f0ef39e77934b5
Version: 45d9bcda21f4c13be75e3571b0f0ef39e77934b5
Version: 45d9bcda21f4c13be75e3571b0f0ef39e77934b5
Version: 45d9bcda21f4c13be75e3571b0f0ef39e77934b5
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{
  "containers": {
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          "product": "Linux",
          "programFiles": [
            "net/netfilter/nft_ct.c",
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      "cpeApplicability": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "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"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerable code is reached by installing crafted nftables/netfilter rules through NETLINK_NETFILTER and then triggering packet evaluation locally. Remote packets alone cannot install the rule, so this is a local attack vector.\nAC:L - A single crafted rule sequence such as `ct zone set` followed by `ct original saddr` can deterministically trigger the bug on matching packets. No race or external condition beyond the attacker\u0027s control is required.\nPR:L - Rule creation requires CAP_NET_ADMIN for the relevant network namespace via nfnetlink. Because nftables is reachable with CAP_NET_ADMIN in a user-created network namespace on systems permitting unprivileged user namespaces, this is low privileges rather than high.\nUI:N - After the attacker installs the crafted rule, triggering occurs through packet processing without any victim user action. No user needs to open a file, mount anything, or interact with attacker-controlled content.\nS:U - The bug corrupts kernel memory during kernel packet-filter evaluation and impacts the same kernel security authority. This is standard kernel privilege escalation/DoS behavior, not a VM, IOMMU, or distinct security-scope escape.\nC:H - The bug is a kernel stack out-of-bounds write past `struct nft_regs`, a memory corruption primitive. Under the required higher-severity rule, such memory corruption is defensibly treated as capable of enabling high confidentiality impact.\nI:H - The vulnerable 16-byte memcpy can overwrite beyond the validated destination register on the kernel stack. Out-of-bounds kernel writes are high integrity impact because they can plausibly be developed into control-flow or privilege-modification primitives.\nA:H - The stack overwrite can corrupt adjacent stack state or registers during packet evaluation and can crash or oops the kernel. Kernel crash or panic is high availability impact."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:34:44.447Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/af80f78ce984649e1698b841cd33f4fa505ad828"
        },
        {
          "url": "https://git.kernel.org/stable/c/8470f676eadeab99132708acb1a85915664d6115"
        },
        {
          "url": "https://git.kernel.org/stable/c/f071b0bf078146368d18e4eec386bf2ddc0ab7e0"
        },
        {
          "url": "https://git.kernel.org/stable/c/2e154b5f53f1b0b490c7b8b02499f90feb86b1d5"
        },
        {
          "url": "https://git.kernel.org/stable/c/3027ecbdb5fdf9200251c21d4818e4c447ef78e1"
        }
      ],
      "title": "netfilter: nft_ct: bail out on template ct in get eval",
      "x_generator": {
        "engine": "bippy-1.2.0"
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  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-53267",
    "datePublished": "2026-06-25T08:39:53.852Z",
    "dateReserved": "2026-06-09T07:44:35.395Z",
    "dateUpdated": "2026-08-05T12:34:44.447Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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