CVE-2026-31421

MEDIUMNVD 5.55.5—
EchelonGraph scoreMEDIUM confidence

Score 5.5 from GitHub Security Advisory published 2026-04-13. NVD baseline CVSS 5.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
5.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.5Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
5.5
EG Score
5.5(medium)
EG Risk
29(Track)
EG Risk 29/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity55% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
2%
KEV
Not listed

Published

April 13, 2026

Last Modified

July 14, 2026

Advisory Details (10)

Auto-updated Jul 19, 2026
⚠️ Active exploitation confirmed. No patch confirmed yet.
generic🔴 Active Exploitation

SSA-082556

https://cert-portal.siemens.com/productcert/html/ssa-082556.html
generic

SSA-019113

https://cert-portal.siemens.com/productcert/html/ssa-019113.html
generic

net/sched: cls_fw: fix NULL pointer dereference on shared blocks - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/febf64ca79a2d6540ab6e5e197fa0f4f7e84473e
generic

net/sched: cls_fw: fix NULL pointer dereference on shared blocks - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/faeea8bbf6e958bf3c00cb08263109661975987c
generic

net/sched: cls_fw: fix NULL pointer dereference on shared blocks - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/d6d5bd62a09650856e1e2010eb09853eba0d64e1
generic

net/sched: cls_fw: fix NULL pointer dereference on shared blocks - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/96426c348def662b06bfdc65be3002905604927a
generic

net/sched: cls_fw: fix NULL pointer dereference on shared blocks - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/5cf41031922c154aa5ccda8bcdb0f5e6226582ec
generic

net/sched: cls_fw: fix NULL pointer dereference on shared blocks - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/3d41f9a314afa94b1c7c7c75405920123220e8cd
generic

net/sched: cls_fw: fix NULL pointer dereference on shared blocks - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/3cb055df9e8625ce699a259d8178d67b37f2b160
generic

net/sched: cls_fw: fix NULL pointer dereference on shared blocks - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28

Vendor Advisories for CVE-2026-31421(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
linuxKernel @ 5.10.253—osv

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(5 across 4 ecosystems)
Debian:11(2)
PackageVulnerable rangeFixed inDependents
linux5.10.103-1 ... 5.10.92-2 (53 versions)5.10.257-1—
linux-6.16.1.106-3~deb11u1 ... 6.1.164-1~deb11u1 (16 versions)6.1.170-1~deb11u1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
linux6.1.106-1 ... 6.1.99-1 (48 versions)6.1.170-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
linux6.12.38-1 ... 6.12.85-1~bpo12+1 (17 versions)6.12.85-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
linux6.12.100-1 ... 6.19~rc8-1~exp1 (122 versions)6.19.12-1—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(24)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 7× in last 7d / 47× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 196 total refreshes for this CVE.

  1. 2026-09-04 05:06 UTCEPSS rescore
  2. 2026-09-02 14:11 UTCEPSS rescore
  3. 2026-09-02 05:28 UTCOSV refresh
  4. 2026-09-01 13:53 UTCEPSS rescore
  5. 2026-09-01 04:39 UTCEPSS rescore
  6. 2026-09-01 04:39 UTCEPSS rescore
  7. 2026-08-30 19:17 UTCEPSS rescore
  8. 2026-08-28 21:41 UTCEPSS rescore
  9. 2026-08-27 14:25 UTCEPSS rescore
  10. 2026-08-26 14:46 UTCEPSS rescore
  11. 2026-08-25 13:49 UTCEPSS rescore
  12. 2026-08-24 14:17 UTCEPSS rescore
  13. 2026-08-23 00:19 UTCEPSS rescore
  14. 2026-08-20 22:55 UTCEPSS rescore
  15. 2026-08-20 22:55 UTCEPSS rescore
  16. 2026-08-19 17:03 UTCEPSS rescore
  17. 2026-08-18 13:48 UTCEPSS rescore
  18. 2026-08-16 14:56 UTCEPSS rescore
  19. 2026-08-16 06:55 UTCEG score recompute
  20. 2026-08-16 06:55 UTCVendor advisory
  21. 2026-08-16 06:55 UTCGHSA enrichment
  22. 2026-08-16 02:14 UTCEPSS rescore
  23. 2026-08-15 01:30 UTCEPSS rescore
  24. 2026-08-14 04:56 UTCEG score recompute
  25. 2026-08-14 04:56 UTCVendor advisory
Show 75 more
  1. 2026-08-14 04:56 UTCGHSA enrichment
  2. 2026-08-13 22:00 UTCEPSS rescore
  3. 2026-08-12 19:10 UTCEG score recompute
  4. 2026-08-12 19:10 UTCVendor advisory
  5. 2026-08-12 19:10 UTCGHSA enrichment
  6. 2026-08-12 13:50 UTCEPSS rescore
  7. 2026-08-11 06:27 UTCEG score recompute
  8. 2026-08-11 06:27 UTCVendor advisory
  9. 2026-08-11 06:27 UTCGHSA enrichment
  10. 2026-08-11 00:00 UTCEPSS rescore
  11. 2026-08-10 05:23 UTCEG score recompute
  12. 2026-08-10 05:23 UTCVendor advisory
  13. 2026-08-10 05:23 UTCGHSA enrichment
  14. 2026-08-09 13:46 UTCEPSS rescore
  15. 2026-08-09 04:20 UTCEG score recompute
  16. 2026-08-09 04:20 UTCVendor advisory
  17. 2026-08-09 04:20 UTCGHSA enrichment
  18. 2026-08-08 16:37 UTCEPSS rescore
  19. 2026-08-07 14:00 UTCEG score recompute
  20. 2026-08-07 14:00 UTCVendor advisory
  21. 2026-08-07 14:00 UTCGHSA enrichment
  22. 2026-08-06 13:46 UTCEPSS rescore
  23. 2026-08-05 23:35 UTCEG score recompute
  24. 2026-08-05 23:35 UTCVendor advisory
  25. 2026-08-05 23:34 UTCGHSA enrichment
  26. 2026-08-05 19:17 UTCEPSS rescore
  27. 2026-08-04 15:10 UTCEPSS rescore
  28. 2026-08-03 21:49 UTCEG score recompute
  29. 2026-08-03 21:49 UTCVendor advisory
  30. 2026-08-03 21:49 UTCGHSA enrichment
  31. 2026-08-03 10:36 UTCEPSS rescore
  32. 2026-08-02 13:34 UTCEG score recompute
  33. 2026-08-02 13:34 UTCVendor advisory
  34. 2026-08-02 13:34 UTCGHSA enrichment
  35. 2026-08-02 02:27 UTCEPSS rescore
  36. 2026-08-01 04:16 UTCEPSS rescore
  37. 2026-07-30 16:27 UTCEPSS rescore
  38. 2026-07-28 15:36 UTCEPSS rescore
  39. 2026-07-26 14:54 UTCEPSS rescore
  40. 2026-07-26 14:54 UTCEPSS rescore
  41. 2026-07-25 14:18 UTCEPSS rescore
  42. 2026-07-25 14:17 UTCEPSS rescore
  43. 2026-07-24 14:17 UTCEPSS rescore
  44. 2026-07-23 14:18 UTCEPSS rescore
  45. 2026-07-23 14:18 UTCEPSS rescore
  46. 2026-07-23 03:08 UTCEG score recompute
  47. 2026-07-22 14:08 UTCEPSS rescore
  48. 2026-07-22 14:08 UTCEPSS rescore
  49. 2026-07-21 15:24 UTCEPSS rescore
  50. 2026-07-21 15:24 UTCEPSS rescore
  51. 2026-07-20 17:08 UTCEPSS rescore
  52. 2026-07-20 17:08 UTCEPSS rescore
  53. 2026-07-20 12:02 UTCOSV refresh
  54. 2026-07-19 14:31 UTCEPSS rescore
  55. 2026-07-19 14:31 UTCEPSS rescore
  56. 2026-07-19 02:29 UTCEPSS rescore
  57. 2026-07-18 10:04 UTCEPSS rescore
  58. 2026-07-18 10:04 UTCEPSS rescore
  59. 2026-07-16 17:03 UTCEPSS rescore
  60. 2026-07-16 17:03 UTCEPSS rescore
  61. 2026-07-15 16:57 UTCEPSS rescore
  62. 2026-07-15 16:57 UTCEPSS rescore
  63. 2026-07-15 02:00 UTCEPSS rescore
  64. 2026-07-15 02:00 UTCEPSS rescore
  65. 2026-07-14 13:19 UTCNVD updateCVSS v3 → 5.5 · severity → MEDIUM
  66. 2026-07-14 13:11 UTCMITRE cvelistV5
  67. 2026-07-13 22:30 UTCEPSS rescore
  68. 2026-07-13 06:13 UTCEPSS rescore
  69. 2026-07-13 06:13 UTCEPSS rescore
  70. 2026-07-12 05:46 UTCEPSS rescore
  71. 2026-07-11 08:27 UTCEPSS rescore
  72. 2026-07-09 19:10 UTCEPSS rescore
  73. 2026-07-08 15:15 UTCEPSS rescore
  74. 2026-07-07 13:46 UTCEPSS rescore
  75. 2026-07-06 16:27 UTCEPSS rescore

Frequently asked(5)

What is CVE-2026-31421?
CVE-2026-31421 is a medium vulnerability published on April 13, 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 fwclassify() calls tcfblock_q() and dereferences q->handle. Shared blocks leave block->q NULL, causing a NULL deref when an empty cls_fw filter…
When was CVE-2026-31421 disclosed?
CVE-2026-31421 was first published in the National Vulnerability Database on April 13, 2026, with the most recent update on July 14, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-31421 actively exploited?
CVE-2026-31421 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 98.0% of all scored CVEs.
What is the CVSS score of CVE-2026-31421?
CVE-2026-31421 has a CVSS v3 base score of 5.5 (NVD).
How do I remediate CVE-2026-31421?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-31421, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-31421

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