high CVSS 7.1

CVE-2021-46993·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: sched: Fix out-of-bound access in uclamp Util-clamp places tasks in different buckets based on their clamp values for performance reasons. However, the size of buckets is currently computed using a rounding division, which can lead to an off-by-one error in some configurations. For instance, with 20 buckets, the bucket size will be 1024/20=51. A task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly, correct indexes are in range [0,19], hence leading to an out of bound memory access. Clamp the bucket id to fix the issue.

Severity
high
Software
Kernel
Fixed in
5.12.5
Published
2024-02-28

Affected versions

From: 5.12

Until: 5.12.5

Fixed in: 5.12.5

How to fix this CVE

Update your Linux kernel to version 5.12.5 or later to address an out-of-bounds memory access vulnerability in the util-clamp scheduler subsystem. This flaw can cause kernel crashes or information disclosure when task scheduling clamp values are miscalculated. Apply the update immediately, especially on systems handling security-sensitive workloads.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check your current kernel version with `uname -r` and verify it is 5.12.5 or later
  2. Step 2: Confirm the util-clamp feature is active by checking `cat /proc/sys/kernel/sched_util_clamp_max` (non-zero output indicates the component is in use)
  3. Step 3: Search kernel logs for out-of-bounds access warnings with `dmesg | grep -i 'out of bounds\|oob\|invalid access'` or `journalctl -xe | grep -i 'sched\|clamp'`
  4. Step 4: After patching, reboot and verify the new kernel version with `uname -r`, then confirm no scheduling-related errors appear in `dmesg` over the next 24 hours

FAQ

What is CVE-2021-46993?

This vulnerability is an array indexing error in the Linux kernel's util-clamp scheduler feature, where task clamp values can be mapped to out-of-bounds bucket indices, potentially causing memory corruption or denial of service.

Is CVE-2021-46993 being actively exploited?

No, this vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog and has no public exploit code available. It is primarily a stability issue rather than an attack vector.

What versions of Kernel are affected by CVE-2021-46993?

Linux kernel versions 5.12 through 5.12.4 are vulnerable. Version 5.12.5 and all subsequent releases contain the fix.

How do I check if my server is vulnerable to CVE-2021-46993?

Run `uname -r` and check if the output shows a version between 5.12 and 5.12.4. If your version is 5.12.5 or higher, you are not vulnerable.

Does Defensia detect CVE-2021-46993?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-46993 will appear in your dashboard with remediation steps.

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References

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