# CVE-2021-47281: linux: In the Linux kernel, the following vulnerability has been resolved:  ALSA: seq: Fix race of snd_seq_timer_open()  The...

CVE-2021-47281 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47281, released May 21, 2024. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-47281
- Priority: High
- CVSS: 7.0 (high)
- EPSS: 0.0024
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 21, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  ALSA: seq: Fix race of snd_seq_timer_open()  The timer instance per queue is exclusive, and snd_seq_timer_open() should have managed the concurrent accesses.  It looks as if it's checking the already existing timer instance at the beginning, but it's not right, because there is no protection, hence any later concurrent call of snd_seq_timer_open() may override the timer instance easily.  This may result in UAF, as the leftover timer instance can keep running while the queue itself gets closed, as spotted by syzkaller recently.  For avoiding the race, add a proper check at the assignment of tmr->timeri again, and return -EBUSY if it's been already registered.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.10.46-1 | [DEBIAN-CVE-2021-47281](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47281.md) | May 21, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.10.46-1 | [DEBIAN-CVE-2021-47281](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47281.md) | May 21, 2024 |
| Linux | linux Debian 14 | 5.10.46-1 | [DEBIAN-CVE-2021-47281](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47281.md) | May 21, 2024 |

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