GHSA-JH9M-9MR6-3GHC

Vulnerability from github – Published: 2026-02-13 15:30 – Updated: 2026-09-03 15:31
VLAI
Details

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

netfilter: nf_tables: fix inverted genmask check in nft_map_catchall_activate()

nft_map_catchall_activate() has an inverted element activity check compared to its non-catchall counterpart nft_mapelem_activate() and compared to what is logically required.

nft_map_catchall_activate() is called from the abort path to re-activate catchall map elements that were deactivated during a failed transaction. It should skip elements that are already active (they don't need re-activation) and process elements that are inactive (they need to be restored). Instead, the current code does the opposite: it skips inactive elements and processes active ones.

Compare the non-catchall activate callback, which is correct:

nft_mapelem_activate(): if (nft_set_elem_active(ext, iter->genmask)) return 0; / skip active, process inactive /

With the buggy catchall version:

nft_map_catchall_activate(): if (!nft_set_elem_active(ext, genmask)) continue; / skip inactive, process active /

The consequence is that when a DELSET operation is aborted, nft_setelem_data_activate() is never called for the catchall element. For NFT_GOTO verdict elements, this means nft_data_hold() is never called to restore the chain->use reference count. Each abort cycle permanently decrements chain->use. Once chain->use reaches zero, DELCHAIN succeeds and frees the chain while catchall verdict elements still reference it, resulting in a use-after-free.

This is exploitable for local privilege escalation from an unprivileged user via user namespaces + nftables on distributions that enable CONFIG_USER_NS and CONFIG_NF_TABLES.

Fix by removing the negation so the check matches nft_mapelem_activate(): skip active elements, process inactive ones.

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-2026-23111"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-416",
      "CWE-672"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-02-13T14:16:10Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nf_tables: fix inverted genmask check in nft_map_catchall_activate()\n\nnft_map_catchall_activate() has an inverted element activity check\ncompared to its non-catchall counterpart nft_mapelem_activate() and\ncompared to what is logically required.\n\nnft_map_catchall_activate() is called from the abort path to re-activate\ncatchall map elements that were deactivated during a failed transaction.\nIt should skip elements that are already active (they don\u0027t need\nre-activation) and process elements that are inactive (they need to be\nrestored). Instead, the current code does the opposite: it skips inactive\nelements and processes active ones.\n\nCompare the non-catchall activate callback, which is correct:\n\n  nft_mapelem_activate():\n    if (nft_set_elem_active(ext, iter-\u003egenmask))\n        return 0;   /* skip active, process inactive */\n\nWith the buggy catchall version:\n\n  nft_map_catchall_activate():\n    if (!nft_set_elem_active(ext, genmask))\n        continue;   /* skip inactive, process active */\n\nThe consequence is that when a DELSET operation is aborted,\nnft_setelem_data_activate() is never called for the catchall element.\nFor NFT_GOTO verdict elements, this means nft_data_hold() is never\ncalled to restore the chain-\u003euse reference count. Each abort cycle\npermanently decrements chain-\u003euse. Once chain-\u003euse reaches zero,\nDELCHAIN succeeds and frees the chain while catchall verdict elements\nstill reference it, resulting in a use-after-free.\n\nThis is exploitable for local privilege escalation from an unprivileged\nuser via user namespaces + nftables on distributions that enable\nCONFIG_USER_NS and CONFIG_NF_TABLES.\n\nFix by removing the negation so the check matches nft_mapelem_activate():\nskip active elements, process inactive ones.",
  "id": "GHSA-jh9m-9mr6-3ghc",
  "modified": "2026-09-03T15:31:30Z",
  "published": "2026-02-13T15:30:26Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23111"
    },
    {
      "type": "WEB",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-23111.json"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f41c5d151078c5348271ffaf8e7410d96f2d82f8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b9b6573421de51829f7ec1cce76d85f5f6fbbd7f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8c760ba4e36c750379d13569f23f5a6e185333f5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8b68a45f9722f2babe9e7bad00aa74638addf081"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/42c574c1504aa089a0a142e4c13859327570473d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1444ff890b4653add12f734ffeffc173d42862dd"
    },
    {
      "type": "WEB",
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-253495.html"
    },
    {
      "type": "WEB",
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-082556.html"
    },
    {
      "type": "WEB",
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
    },
    {
      "type": "WEB",
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2439687"
    },
    {
      "type": "WEB",
      "url": "https://blog.exodusintel.com/2026/06/08/off-by-exploiting-a-use-after-free-in-the-linux-kernel"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/security/cve/CVE-2026-23111"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:9112"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:6570"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:62641"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:62639"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:18134"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:10996"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:10108"
    }
  ],
  "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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