{
  "affected": [
    {
      "ranges": [
        {
          "events": [
            {
              "introduced": "1abf272022cf1d18469405f47b4ec49c6a3125db"
            },
            {
              "fixed": "d6d5bd62a09650856e1e2010eb09853eba0d64e1"
            },
            {
              "fixed": "febf64ca79a2d6540ab6e5e197fa0f4f7e84473e"
            },
            {
              "fixed": "3d41f9a314afa94b1c7c7c75405920123220e8cd"
            },
            {
              "fixed": "18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28"
            },
            {
              "fixed": "5cf41031922c154aa5ccda8bcdb0f5e6226582ec"
            },
            {
              "fixed": "3cb055df9e8625ce699a259d8178d67b37f2b160"
            },
            {
              "fixed": "96426c348def662b06bfdc65be3002905604927a"
            },
            {
              "fixed": "faeea8bbf6e958bf3c00cb08263109661975987c"
            }
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "type": "GIT"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Linux",
        "name": "Kernel"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.15.0"
            },
            {
              "fixed": "5.10.253"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "5.11.0"
            },
            {
              "fixed": "5.15.203"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "5.16.0"
            },
            {
              "fixed": "6.1.168"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.2.0"
            },
            {
              "fixed": "6.6.134"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.7.0"
            },
            {
              "fixed": "6.12.81"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.13.0"
            },
            {
              "fixed": "6.18.22"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.19.0"
            },
            {
              "fixed": "6.19.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Linux",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31421.json"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: cls_fw: fix NULL pointer dereference on shared blocks\n\nThe old-method path in fw_classify() calls tcf_block_q() and\ndereferences q-\u003ehandle.  Shared blocks leave block-\u003eq NULL, causing a\nNULL deref when an empty cls_fw filter is attached to a shared block\nand a packet with a nonzero major skb mark is classified.\n\nReject the configuration in fw_change() when the old method (no\nTCA_OPTIONS) is used on a shared block, since fw_classify()'s\nold-method path needs block-\u003eq which is NULL for shared blocks.\n\nThe fixed null-ptr-deref calling stack:\n KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f]\n RIP: 0010:fw_classify (net/sched/cls_fw.c:81)\n Call Trace:\n  tcf_classify (./include/net/tc_wrapper.h:197 net/sched/cls_api.c:1764 net/sched/cls_api.c:1860)\n  tc_run (net/core/dev.c:4401)\n  __dev_queue_xmit (net/core/dev.c:4535 net/core/dev.c:4790)",
  "id": "CVE-2026-31421",
  "modified": "2026-07-08T05:36:40.759469068Z",
  "published": "2026-04-13T13:40:25.278Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3cb055df9e8625ce699a259d8178d67b37f2b160"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3d41f9a314afa94b1c7c7c75405920123220e8cd"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5cf41031922c154aa5ccda8bcdb0f5e6226582ec"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/96426c348def662b06bfdc65be3002905604927a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d6d5bd62a09650856e1e2010eb09853eba0d64e1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/faeea8bbf6e958bf3c00cb08263109661975987c"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/febf64ca79a2d6540ab6e5e197fa0f4f7e84473e"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31421.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31421"
    },
    {
      "type": "PACKAGE",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
    }
  ],
  "schema_version": "1.7.5",
  "summary": "net/sched: cls_fw: fix NULL pointer dereference on shared blocks"
}