CVE-2021-47396
mac80211-hwsim: fix late beacon hrtimer handling
- Published
- Updated
- Reserved
- Assigned by
- Linux
Description
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.
Timeline
ID reserved
By Linux
Published
- 24 months later
· 24 months later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| NVDNVD · Analyzed | 3.1 | Medium5.5 | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.24% · top 85% of all CVEs (7 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.
Affected products
- affected 01e59e467ecf976c782eecd4dc99644802cc60e2 – < 9bee85de2c8155388c09a2e1530a243ec1c96f05
- affected 01e59e467ecf976c782eecd4dc99644802cc60e2 – < 2c204cf594df3b9468368dc9d0b24d482d93cda7
- affected 01e59e467ecf976c782eecd4dc99644802cc60e2 – < ed2adf69e29848d1eb9df99633dde655421c92ed
- affected 01e59e467ecf976c782eecd4dc99644802cc60e2 – < 313bbd1990b6ddfdaa7da098d0c56b098a833572
- affected 3.9
- unaffected < 3.9
- unaffected 5.4.151 – ≤ 5.4.*
- unaffected 5.10.71 – ≤ 5.10.*
- unaffected 5.14.10 – ≤ 5.14.*
- unaffected 5.15 – ≤ *
References (4)
- https://git.kernel.org/stable/c/9bee85de2c8155388c09a2e1530a243ec1c96f05 (opens in a new tab)x_transferred
- https://git.kernel.org/stable/c/2c204cf594df3b9468368dc9d0b24d482d93cda7 (opens in a new tab)x_transferred
- https://git.kernel.org/stable/c/ed2adf69e29848d1eb9df99633dde655421c92ed (opens in a new tab)x_transferred
- https://git.kernel.org/stable/c/313bbd1990b6ddfdaa7da098d0c56b098a833572 (opens in a new tab)x_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2021-47396)Record last updated .