CVE-2021-46936

HIGHNVD 7.87.8—
EchelonGraph scoreMEDIUM confidence

Score 7.8 from GitHub Security Advisory (severity: HIGH) published 2024-02-27. NVD baseline CVSS 7.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 4 sources updated this week
7.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.8Exploit: None knownExposed: 0

A fix is available — apply it.

In the Linux kernel, the following vulnerability has been resolved:

net: fix use-after-free in tw_timer_handler

A real world panic issue was found as follow in Linux 5.4.

BUG: unable to handle page fault for address: ffffde49a863de28 PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0 RIP: 0010:tw_timer_handler+0x20/0x40 Call Trace: call_timer_fn+0x2b/0x120 run_timer_softirq+0x1ef/0x450 __do_softirq+0x10d/0x2b8 irq_exit+0xc7/0xd0 smp_apic_timer_interrupt+0x68/0x120 apic_timer_interrupt+0xf/0x20

This issue was also reported since 2017 in the thread [1], unfortunately, the issue was still can be reproduced after fixing DCCP.

The ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net namespace is destroyed since tcp_sk_ops is registered befrore ipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops in the list of pernet_list. There will be a use-after-free on net->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net if there are some inflight time-wait timers.

This bug is not introduced by commit f2bf415cfed7 ("mib: add net to NET_ADD_STATS_BH") since the net_statistics is a global variable instead of dynamic allocation and freeing. Actually, commit 61a7e26028b9 ("mib: put net statistics on struct net") introduces the bug since it put net statistics on struct net and free it when net namespace is destroyed.

Moving init_ipv4_mibs() to the front of tcp_init() to fix this bug and replace pr_crit() with panic() since continuing is meaningless when init_ipv4_mibs() fails.

[1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1

CVSS v3
7.8
EG Score
7.8(medium)
EG Risk
35(Track)
EG Risk 35/100SSVC: 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
Severity78% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
16%
KEV
Not listed

Published

February 27, 2024

Last Modified

August 5, 2026

Advisory Details (8)

Auto-updated Aug 4, 2026
No patch confirmed yet.
generic

net: fix use-after-free in tw_timer_handler - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022
generic

net: fix use-after-free in tw_timer_handler - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13
generic

net: fix use-after-free in tw_timer_handler - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69
generic

net: fix use-after-free in tw_timer_handler - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a
generic

net: fix use-after-free in tw_timer_handler - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0
generic

net: fix use-after-free in tw_timer_handler - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566
generic

net: fix use-after-free in tw_timer_handler - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4
generic

net: fix use-after-free in tw_timer_handler - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-virtual-lts-xenial (4.4.0.253.259) @ xenial2026-05-24ubuntu

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.

Weakness Classification(1)

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

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 15× 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 126 total refreshes for this CVE.

  1. 2026-08-07 16:24 UTCEPSS rescore
  2. 2026-08-06 13:44 UTCEPSS rescore
  3. 2026-08-05 19:15 UTCEPSS rescore
  4. 2026-08-05 09:46 UTCEG score recompute
  5. 2026-08-05 09:46 UTCGHSA enrichment
  6. 2026-08-04 15:06 UTCEPSS rescore
  7. 2026-08-04 12:22 UTCEG score recompute
  8. 2026-08-04 12:22 UTCVendor advisory
  9. 2026-08-04 12:22 UTCGHSA enrichment
  10. 2026-08-04 10:34 UTCEPSS rescore
  11. 2026-08-04 09:55 UTCEG score recompute
  12. 2026-08-04 09:55 UTCVendor advisory
  13. 2026-08-04 09:55 UTCGHSA enrichment
  14. 2026-08-03 10:33 UTCEPSS rescore
  15. 2026-08-02 02:24 UTCEPSS rescore
  16. 2026-08-01 11:36 UTCOSV refresh
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  1. 2026-07-23 02:06 UTCEG score recompute
  2. 2026-07-22 22:52 UTCEG score recompute
  3. 2026-07-22 14:06 UTCEPSS rescore
  4. 2026-07-21 15:22 UTCEPSS rescore
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  6. 2026-07-20 17:05 UTCEPSS rescore
  7. 2026-07-19 02:27 UTCEPSS rescore
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  13. 2026-07-15 01:58 UTCEPSS rescore
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  15. 2026-07-14 18:55 UTCOSV refresh
  16. 2026-07-13 22:27 UTCEPSS rescore
  17. 2026-07-13 06:11 UTCEPSS rescore
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  19. 2026-07-12 05:44 UTCEPSS rescore
  20. 2026-07-11 08:25 UTCEPSS rescore
  21. 2026-07-09 19:07 UTCEPSS rescore
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  23. 2026-07-08 15:12 UTCEPSS rescore
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  25. 2026-07-07 13:43 UTCEPSS rescore
  26. 2026-07-06 16:25 UTCEPSS rescore
  27. 2026-07-06 16:25 UTCEPSS rescore
  28. 2026-07-06 02:21 UTCEPSS rescore
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  41. 2026-06-27 03:07 UTCEPSS rescore
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  43. 2026-06-26 19:39 UTCOSV refresh
  44. 2026-06-25 13:48 UTCEPSS rescore
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  46. 2026-06-24 14:03 UTCEPSS rescore
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  48. 2026-06-23 21:31 UTCEPSS rescore
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  50. 2026-06-22 14:24 UTCEPSS rescore
  51. 2026-06-21 14:55 UTCEPSS rescore
  52. 2026-06-21 01:58 UTCEPSS rescore
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  54. 2026-06-19 19:24 UTCEPSS rescore
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  56. 2026-06-18 17:51 UTCEPSS rescore
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  67. 2026-06-11 13:58 UTCEPSS rescore
  68. 2026-06-10 22:16 UTCEPSS rescore
  69. 2026-06-09 04:30 UTCOSV refresh
  70. 2026-06-08 14:15 UTCEPSS rescore
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  73. 2026-06-07 15:23 UTCEPSS rescore
  74. 2026-06-07 15:23 UTCEPSS rescore
  75. 2026-06-06 13:46 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2021-46936?
CVE-2021-46936 is a high vulnerability published on February 27, 2024. In the Linux kernel, the following vulnerability has been resolved: net: fix use-after-free in twtimerhandler A real world panic issue was found as follow in Linux 5.4. BUG: unable to handle page fault for address: ffffde49a863de28 PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0…
When was CVE-2021-46936 disclosed?
CVE-2021-46936 was first published in the National Vulnerability Database on February 27, 2024, with the most recent update on August 5, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-46936 actively exploited?
CVE-2021-46936 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 84.4% of all scored CVEs.
What is the CVSS score of CVE-2021-46936?
CVE-2021-46936 has a CVSS v3 base score of 7.8 (NVD).
How do I remediate CVE-2021-46936?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-46936, 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.

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