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Linux KernelOperating system · Linux

CVE-2021-47393

HIGH · 7.1 CVSS v3.1 Published 2024-05-21
Fix available
A fix is available. Upgrade to 4.19.209 / 5.4.151 or later.
See remediation →
73/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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 ..

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-125

The code reads past the end (or before the start) of a buffer, returning memory that was never meant to be exposed. Attackers use it to leak secrets like keys or to defeat memory-protection defences. Remediation is validating indices and lengths before every read.

General guidance for the out-of-bounds read class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 4.19, < 4.19.209>= 4.20, < 5.4.151>= 5.5, < 5.10.71>= 5.11, < 5.14.10= 5.15

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.19.209 / 5.4.151 / 5.10.71 or later
Fixed in 4.19.2095.4.1515.10.71
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux Kernel 4.19.209 / 5.4.151 / 5.10.71 / 5.14.10 (depending on your major version branch)

  1. Identify the currently running Linux kernel version using `uname -r`
  2. Determine which version range the current kernel falls into (4.19.x, 4.20-5.4.x, 5.5-5.10.x, or 5.11-5.14.x)
  3. Upgrade the Linux kernel to the first fixed version in that range: 4.19.209, 5.4.151, 5.10.71, or 5.14.10 respectively
  4. Reboot the system to apply the new kernel
  5. Verify the kernel version after reboot using `uname -r`
Caveat Standard kernel upgrade risks - ensure compatibility with existing system configuration and drivers before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

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Peer-ranked notes from engineers who’ve handled CVE-2021-47393 in production — separate from our analysis above.

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