CVE-2021-47396

Medium

In the Linux kernel, the following vulnerability has been resolved: mac80211-hwsim: fix late beacon hrtimer handling Thomas explained in https://lore.kernel.org/r/87mtoeb4hb.ffs@tglx that our handling of the hrtimer here is wrong: If the timer fires late (e.g. due to vCPU scheduling, as reported by Dmitry/syzbot) then it tries to actually rearm the timer at the next deadline, which might be in the past already: 1 2 3 N N+1 | | | ... | | ^ intended to fire here (1) ^ next deadline here (2) ^ actually fired here The next time it fires, it's later, but will still try to schedule for the next deadline (now 3), etc. until it catches up with N, but that might take a long time, causing stalls etc. Now, all of this is simulation, so we just have to fix it, but note that the behaviour is wrong even per spec, since there's no value then in sending all those beacons unaligned - they should be aligned to the TBTT (1, 2, 3, ... in the picture), and if we're a bit (or a lot) late, then just resume at that point. Therefore, change the code to use hrtimer_forward_now() which will ensure that the next firing of the timer would be at N+1 (in the picture), i.e. the next interval point after the current time.

Package Linux Kernel
Published 2024-05-21
Last modified 2025-09-25
CVSS version 3.1
Patch available
Yes

CVSS 3.1 score

5.5

out of 10
Medium
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
High
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected versions

Linux kernel versions 3.9 and later are affected. Fixed in 5.4.151, 5.10.71, 5.14.10, 5.15 and their respective stable series.

Affected from
≥ 3.9
Fixed in
✓ 5.4.151 5.4.x ✓ 5.10.71 5.10.x ✓ 5.14.10 5.14.x ✓ 5.15

References

4 total

Frequently asked questions

  • What is CVE-2021-47396?

    CVE-2021-47396 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10 . It affects Linux kernel versions from 3.9 onward and has been patched in 5.4.151, 5.10.71, 5.14.10 and others. CVE-2021-47396 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2021-47396?

    CVE-2021-47396 has a CVSS score of 5.5 out of 10, rated Medium severity (CVSS 3.1). The vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H .

  • Is there a patch available for CVE-2021-47396?

    Yes. CVE-2021-47396 has been patched. Fixed versions include 5.4.151, 5.10.71, 5.14.10 and others. If you are running Linux kernel 3.9 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2021-47396 actively exploited?

    No. CVE-2021-47396 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

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