# CVE-2021-47393: hwmon: (mlxreg-fan) Return non-zero value when fan current state is enforced from sysfs

> A local attacker can trigger a slab-out-of-bounds read in the Linux kernel thermal subsystem, potentially causing a system crash.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 May 2024
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2021-47393, GHSA-7f2x-rjqg-7667, UBUNTU-CVE-2021-47393

## What is CVE-2021-47393?

CVE-2021-47393 is a high-severity memory corruption vulnerability in Linux kernel, published on 21 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

hwmon: (mlxreg-fan) Return non-zero value when fan current state is enforced from sysfs

Fan speed minimum can be enforced from sysfs. For example, setting
current fan speed to 20 is used to enforce fan speed to be at 100%
speed, 19 - to be not below 90% speed, etcetera. This feature provides
ability to limit fan speed according to some system wise
considerations, like absence of some replaceable units or high system
ambient temperature.

Request for changing fan minimum speed is configuration request and can
be set only through 'sysfs' write procedure. In this situation value of
argument 'state' is above nominal fan speed maximum.

Return non-zero code in this case to avoid
thermal_cooling_device_stats_update() call, because in this case
statistics update violates thermal statistics table range.
The issues is observed in case kernel is configured with option
CONFIG_THERMAL_STATISTICS.

Here is the trace from KASAN:
[  159.506659] BUG: KASAN: slab-out-of-bounds in thermal_cooling_device_stats_update+0x7d/0xb0
[  159.516016] Read of size 4 at addr ffff888116163840 by task hw-management.s/7444
[  159.545625] Call Trace:
[  159.548366]  dump_stack+0x92/0xc1
[  159.552084]  ? thermal_cooling_device_stats_update+0x7d/0xb0
[  159.635869]  thermal_zone_device_update+0x345/0x780
[  159.688711]  thermal_zone_device_set_mode+0x7d/0xc0
[  159.694174]  mlxsw_thermal_modules_init+0x48f/0x590 [mlxsw_core]
[  159.700972]  ? mlxsw_thermal_set_cur_state+0x5a0/0x5a0 [mlxsw_core]
[  159.731827]  mlxsw_thermal_init+0x763/0x880 [mlxsw_core]
[  160.070233] RIP: 0033:0x7fd995909970
[  160.074239] Code: 73 01 c3 48 8b 0d 28 d5 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 99 2d 2c 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ..
[  160.095242] RSP: 002b:00007fff54f5d938 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[  160.103722] RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 00007fd995909970
[  160.111710] RDX: 0000000000000013 RSI: 0000000001906008 RDI: 0000000000000001
[  160.119699] RBP: 0000000001906008 R08: 00007fd995bc9760 R09: 00007fd996210700
[  160.127687] R10: 0000000000000073 R11: 0000000000000246 R12: 0000000000000013
[  160.135673] R13: 0000000000000001 R14: 00007fd995bc8600 R15: 0000000000000013
[  160.143671]
[  160.145338] Allocated by task 2924:
[  160.149242]  kasan_save_stack+0x19/0x40
[  160.153541]  __kasan_kmalloc+0x7f/0xa0
[  160.157743]  __kmalloc+0x1a2/0x2b0
[  160.161552]  thermal_cooling_device_setup_sysfs+0xf9/0x1a0
[  160.167687]  __thermal_cooling_device_register+0x1b5/0x500
[  160.173833]  devm_thermal_of_cooling_device_register+0x60/0xa0
[  160.180356]  mlxreg_fan_probe+0x474/0x5e0 [mlxreg_fan]
[  160.248140]
[  160.249807] The buggy address belongs to the object at ffff888116163400
[  160.249807]  which belongs to the cache kmalloc-1k of size 1024
[  160.263814] The buggy address is located 64 bytes to the right of
[  160.263814]  1024-byte region [ffff888116163400, ffff888116163800)
[  160.277536] The buggy address belongs to the page:
[  160.282898] page:0000000012275840 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888116167000 pfn:0x116160
[  160.294872] head:0000000012275840 order:3 compound_mapcount:0 compound_pincount:0
[  160.303251] flags: 0x200000000010200(slab|head|node=0|zone=2)
[  160.309694] raw: 0200000000010200 ffffea00046f7208 ffffea0004928208 ffff88810004dbc0
[  160.318367] raw: ffff888116167000 00000000000a0006 00000001ffffffff 0000000000000000
[  160.327033] page dumped because: kasan: bad access detected
[  160.333270]
[  160.334937] Memory state around the buggy address:
[  160.356469] >ffff888116163800: fc ..

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2021-47393?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47393?

Apply the vendor's patch.

## Is CVE-2021-47393 being exploited?

There is no known exploitation of CVE-2021-47393 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-47393 and fix it if it is affected.

What it is: CVE-2021-47393 is a high-severity memory corruption vulnerability in Linux kernel, published on 21 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-47393 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-47393/ (Markdown: https://insights.sbomify.com/CVE-2021-47393/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47393
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47393
- OSV: https://osv.dev/vulnerability/CVE-2021-47393

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47393/
Summaries are generated and may contain mistakes; the official description above is the record.