CVE-2026-31421net/sched: cls_fw: fix NULL pointer dereference on shared blocks
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_fw: fix NULL pointer dereference on shared blocks The old-method path in fw_classify() calls tcf_block_q() and dereferences q->handle. Shared blocks leave block->q NULL, causing a NULL deref when an empty cls_fw filter is attached to a shared block and a packet with a nonzero major skb mark is classified. Reject the configuration in fw_change() when the old method (no TCA_OPTIONS) is used on a shared block, since fw_classify()'s old-method path needs block->q which is NULL for shared blocks. The fixed null-ptr-deref calling stack: KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:fw_classify (net/sched/cls_fw.c:81) Call Trace: tcf_classify (./include/net/tc_wrapper.h:197 net/sched/cls_api.c:1764 net/sched/cls_api.c:1860) tc_run (net/core/dev.c:4401) __dev_queue_xmit (net/core/dev.c:4535 net/core/dev.c:4790)
- CVSS
- 5.5 MEDIUM (v3.1, NVD)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- Weakness (CWE)
- Not given
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Linux
- NVD analysis
- Modified
- Record last updated
- Oct 15, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Linux Linux linux:linux (from the name) | from 1abf272022cf1d18469405f47b4ec49c6a3125db before d6d5bd62a09650856e1e2010eb09853eba0d64e1; from 1abf272022cf1d18469405f47b4ec49c6a3125db before febf64ca79a2d6540ab6e5e197fa0f4f7e84473e; from 1abf272022cf1d18469405f47b4ec49c6a3125db before 3d41f9a314afa94b1c7c7c75405920123220e8cd; from 1abf272022cf1d18469405f47b4ec49c6a3125db before 18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28; from 1abf272022cf1d18469405f47b4ec49c6a3125db before 5cf41031922c154aa5ccda8bcdb0f5e6226582ec; from 1abf272022cf1d18469405f47b4ec49c6a3125db before 3cb055df9e8625ce699a259d8178d67b37f2b160; from 1abf272022cf1d18469405f47b4ec49c6a3125db before 96426c348def662b06bfdc65be3002905604927a; from 1abf272022cf1d18469405f47b4ec49c6a3125db before faeea8bbf6e958bf3c00cb08263109661975987c | CNA record |
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518_4_pn_dp_mfp (from the name) | from V3.1.6 | CISA ADP |
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518f_4_pn_dp_mfp (from the name) | from V3.1.6 | CISA ADP |
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP siemens:siplus_s7_1500_cpu_1518_4_pn_dp_mfp (from the name) | from V3.1.6 | CISA ADP |
linux linux_kernel linux:linux_kernel | from 4.15 before 5.10.253; from 5.11 before 5.15.203; from 5.16 before 6.1.168; from 6.2 before 6.6.134; from 6.7 before 6.12.81; from 6.13 before 6.18.22; from 6.19 before 6.19.12; 7.0; and 5 more ranges | NVD |
References
- https://git.kernel.org/stable/c/d6d5bd62a09650856e1e2010eb09853eba0d64e1patch
- https://git.kernel.org/stable/c/febf64ca79a2d6540ab6e5e197fa0f4f7e84473epatch
- https://git.kernel.org/stable/c/3d41f9a314afa94b1c7c7c75405920123220e8cdpatch
- https://git.kernel.org/stable/c/18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28patch
- https://git.kernel.org/stable/c/5cf41031922c154aa5ccda8bcdb0f5e6226582ecpatch
- https://git.kernel.org/stable/c/3cb055df9e8625ce699a259d8178d67b37f2b160patch
- https://git.kernel.org/stable/c/96426c348def662b06bfdc65be3002905604927apatch
- https://git.kernel.org/stable/c/faeea8bbf6e958bf3c00cb08263109661975987cpatch
- https://cert-portal.siemens.com/productcert/html/ssa-019113.html
- https://cert-portal.siemens.com/productcert/html/ssa-082556.html
- https://cert-portal.siemens.com/productcert/html/ssa-457936.html
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.