Answer in brief
CVE-2026-31421 records a Medium severity (CVSS 5.5) vulnerability in net/sched: cls_fw: fix NULL pointer dereference on shared blocks. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
Answer in brief
CVE-2026-31421 records a Medium severity (CVSS 5.5) vulnerability in net/sched: cls_fw: fix NULL pointer dereference on shared blocks. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 5.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=1abf272022cf1d18469405f47b4ec49c6a3125db <d6d5bd62a09650856e1e2010eb09853eba0d64e1 || >=1abf272022cf1d18469405f47b4ec49c6a3125db <febf64ca79a2d6540ab6e5e197fa0f4f7e84473e || >=1abf272022cf1d18469405f47b4ec49c6a3125db <3d41f9a314afa94b1c7c7c75405920123220e8cd || >=1abf272022cf1d18469405f47b4ec49c6a3125db <18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28 || >=1abf272022cf1d18469405f47b4ec49c6a3125db <5cf41031922c154aa5ccda8bcdb0f5e6226582ec || >=1abf272022cf1d18469405f47b4ec49c6a3125db <3cb055df9e8625ce699a259d8178d67b37f2b160 || >=1abf272022cf1d18469405f47b4ec49c6a3125db <96426c348def662b06bfdc65be3002905604927a || >=1abf272022cf1d18469405f47b4ec49c6a3125db <faeea8bbf6e958bf3c00cb08263109661975987c | d6d5bd62a09650856e1e2010eb09853eba0d64e1, febf64ca79a2d6540ab6e5e197fa0f4f7e84473e, 3d41f9a314afa94b1c7c7c75405920123220e8cd, 18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28, 5cf41031922c154aa5ccda8bcdb0f5e6226582ec, 3cb055df9e8625ce699a259d8178d67b37f2b160, 96426c348def662b06bfdc65be3002905604927a, faeea8bbf6e958bf3c00cb08263109661975987c |
| Linux/Linuxgeneric | 4.15 | Not reported |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
Published upstream
Apr 13, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Jul 14, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 14, 2026
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)
Quoted source text, attributed separately from HOL analysis.
CVSS is 5.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=1abf272022cf1d18469405f47b4ec49c6a3125db <d6d5bd62a09650856e1e2010eb09853eba0d64e1 || >=1abf272022cf1d18469405f47b4ec49c6a3125db <febf64ca79a2d6540ab6e5e197fa0f4f7e84473e || >=1abf272022cf1d18469405f47b4ec49c6a3125db <3d41f9a314afa94b1c7c7c75405920123220e8cd || >=1abf272022cf1d18469405f47b4ec49c6a3125db <18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28 || >=1abf272022cf1d18469405f47b4ec49c6a3125db <5cf41031922c154aa5ccda8bcdb0f5e6226582ec || >=1abf272022cf1d18469405f47b4ec49c6a3125db <3cb055df9e8625ce699a259d8178d67b37f2b160 || >=1abf272022cf1d18469405f47b4ec49c6a3125db <96426c348def662b06bfdc65be3002905604927a || >=1abf272022cf1d18469405f47b4ec49c6a3125db <faeea8bbf6e958bf3c00cb08263109661975987c | d6d5bd62a09650856e1e2010eb09853eba0d64e1, febf64ca79a2d6540ab6e5e197fa0f4f7e84473e, 3d41f9a314afa94b1c7c7c75405920123220e8cd, 18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28, 5cf41031922c154aa5ccda8bcdb0f5e6226582ec, 3cb055df9e8625ce699a259d8178d67b37f2b160, 96426c348def662b06bfdc65be3002905604927a, faeea8bbf6e958bf3c00cb08263109661975987c |
| Linux/Linuxgeneric | 4.15 | Not reported |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.5 <* | * |
Published upstream
Apr 13, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Jul 14, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 14, 2026
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)
Quoted source text, attributed separately from HOL analysis.