{"id":"CVE-2026-31421","title":"net/sched: cls_fw: fix NULL pointer dereference on shared blocks","summary":"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->handle.  Shared blocks le…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < d6d5bd62a09650856e1e2010eb09853eba0d64e1","Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < febf64ca79a2d6540ab6e5e197fa0f4f7e84473e","Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 3d41f9a314afa94b1c7c7c75405920123220e8cd","Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28","Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 5cf41031922c154aa5ccda8bcdb0f5e6226582ec","Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 3cb055df9e8625ce699a259d8178d67b37f2b160","Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 96426c348def662b06bfdc65be3002905604927a","Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < faeea8bbf6e958bf3c00cb08263109661975987c","Linux 4.15"],"published":"2026-04-13","updated":"2026-09-08","sourceUpdated":"2026-09-08T08:46:56.901Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31421","references":[{"url":"https://git.kernel.org/stable/c/d6d5bd62a09650856e1e2010eb09853eba0d64e1"},{"url":"https://git.kernel.org/stable/c/febf64ca79a2d6540ab6e5e197fa0f4f7e84473e"},{"url":"https://git.kernel.org/stable/c/3d41f9a314afa94b1c7c7c75405920123220e8cd"},{"url":"https://git.kernel.org/stable/c/18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28"},{"url":"https://git.kernel.org/stable/c/5cf41031922c154aa5ccda8bcdb0f5e6226582ec"},{"url":"https://git.kernel.org/stable/c/3cb055df9e8625ce699a259d8178d67b37f2b160"},{"url":"https://git.kernel.org/stable/c/96426c348def662b06bfdc65be3002905604927a"},{"url":"https://git.kernel.org/stable/c/faeea8bbf6e958bf3c00cb08263109661975987c"}],"tags":["cve.org"],"epss":0.00171,"epssPercentile":0.05674,"ingestedAt":"2026-09-08T15:33:26.991Z","slug":"CVE-2026-31421","body":"## Overview\n\nIn 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->handle.  Shared blocks leave block->q 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->q 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)\n\n## Affected\n\n- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < d6d5bd62a09650856e1e2010eb09853eba0d64e1`\n- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < febf64ca79a2d6540ab6e5e197fa0f4f7e84473e`\n- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 3d41f9a314afa94b1c7c7c75405920123220e8cd`\n- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28`\n- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 5cf41031922c154aa5ccda8bcdb0f5e6226582ec`\n- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 3cb055df9e8625ce699a259d8178d67b37f2b160`\n- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 96426c348def662b06bfdc65be3002905604927a`\n- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < faeea8bbf6e958bf3c00cb08263109661975987c`\n- `Linux 4.15`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}