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Linux KernelOperating system · Linux

CVE-2021-47334

HIGH · 7.8 CVSS v3.1 Published 2024-05-21
Fix available
A fix is available. Upgrade to 4.4.276 / 4.9.276 or later.
See remediation →
80/100
Remediation priority · High
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: misc/libmasm/module: Fix two use after free in ibmasm_init_one In ibmasm_init_one, it calls ibmasm_init_remote_input_dev(). Inside ibmasm_init_remote_input_dev, mouse_dev and keybd_dev are allocated by input_allocate_device(), and assigned to sp->remote.mouse_dev and sp->remote.keybd_dev respectively. In the err_free_devices error branch of ibmasm_init_one, mouse_dev and keybd_dev are freed by input_free_device(), and return error. Then the execution runs into error_send_message error branch of ibmasm_init_one, where ibmasm_free_remote_input_dev(sp) is called to unregister the freed sp->remote.mouse_dev and sp->remote.keybd_dev. My patch add a "error_init_remote" label to handle the error of ibmasm_init_remote_input_dev(), to avoid the uaf bugs.

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-416

Memory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.

General guidance for the use after free 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:< 4.4.276>= 4.5, < 4.9.276>= 4.10, < 4.14.240>= 4.15, < 4.19.198>= 4.20, < 5.4.134>= 5.5, < 5.10.52>= 5.11, < 5.12.19>= 5.13, < 5.13.4

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
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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 4.4.276 / 4.9.276 / 4.14.240 or later
Fixed in 4.4.2764.9.2764.14.240
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux kernel 4.4.276, 4.9.276, 4.14.240, or 4.19.198 (depending on your stable branch)

  1. Obtain the kernel source code for your currently running kernel version
  2. Apply the patch from commit 1512e7dc5eb08b7d92a12e2bfcd9cb8c4a1ec069 which adds an 'error_init_remote' label to handle errors from ibmasm_init_remote_input_dev()
  3. Recompile the kernel with the fix applied
  4. Reboot into the patched kernel
  5. Verify the fix is active by checking the kernel version or the presence of the patched code in /lib/modules/$(uname -r)
Caveat Upgrading kernel versions may require rebuilding out-of-tree kernel modules and could introduce regressions in driver compatibility

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

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-47334 in production — separate from our analysis above.

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What this is

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