CVE-2025-21647

High

In the Linux kernel, the following vulnerability has been resolved: sched: sch_cake: add bounds checks to host bulk flow fairness counts Even though we fixed a logic error in the commit cited below, syzbot still managed to trigger an underflow of the per-host bulk flow counters, leading to an out of bounds memory access. To avoid any such logic errors causing out of bounds memory accesses, this commit factors out all accesses to the per-host bulk flow counters to a series of helpers that perform bounds-checking before any increments and decrements. This also has the benefit of improving readability by moving the conditional checks for the flow mode into these helpers, instead of having them spread out throughout the code (which was the cause of the original logic error). As part of this change, the flow quantum calculation is consolidated into a helper function, which means that the dithering applied to the ost load scaling is now applied both in the DRR rotation and when a sparse flow's quantum is first initiated. The only user-visible effect of this is that the maximum packet size that can be sent while a flow stays sparse will now vary with +/- one byte in some cases. This should not make a noticeable difference in practice, and thus it's not worth complicating the code to preserve the old behaviour.

Package Linux Kernel
Published 2025-01-19
Last modified 2026-05-12
CVSS version 3.1
Patch available
Yes

CVSS 3.1 score

7.1

out of 10
High
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

Weakness type

CWE-125

CVE-2025-21647 is a Out-of-bounds Read vulnerability

What is Out-of-bounds Read?

The product reads data past the end or before the beginning of the intended buffer. Learn more on MITRE CWE

Affected versions

Linux kernel versions 5.4.284, 5.10.226, 5.15.167, 6.1.110, 6.6.51, 6.10.10, 6.11 and later are affected. Fixed in 5.4.291, 5.10.235, 5.15.179, 6.1.125, 6.6.72, 6.12.10, 6.13 and their respective stable series.

Affected from
≥ 5.4.284 ≥ 5.10.226 ≥ 5.15.167 ≥ 6.1.110 ≥ 6.6.51 ≥ 6.10.10 ≥ 6.11
Fixed in
✓ 5.4.291 5.4.x ✓ 5.10.235 5.10.x ✓ 5.15.179 5.15.x ✓ 6.1.125 6.1.x ✓ 6.6.72 6.6.x ✓ 6.12.10 6.12.x ✓ 6.13

References

The following references provide additional information about CVE-2025-21647 including vendor advisories, patch commits, exploit details, and third-party analysis. Links are sourced from the NIST NVD database.

7 patch commits total View all on NVD

Frequently asked questions

  • What is CVE-2025-21647?

    CVE-2025-21647 is a High severity Linux kernel vulnerability with a CVSS score of 7.1 out of 10 , classified as an Out-of-bounds Read flaw (CWE-125) . It affects Linux kernel versions from 5.4.284 onward and has been patched in 5.4.291, 5.10.235, 5.15.179 and others. CVE-2025-21647 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2025-21647?

    CVE-2025-21647 has a CVSS score of 7.1 out of 10, rated High severity (CVSS 3.1). The vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H .

  • Is there a patch available for CVE-2025-21647?

    Yes — CVE-2025-21647 has been patched. Fixed versions include 5.4.291, 5.10.235, 5.15.179 and others. If you are running Linux kernel 5.4.284 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2025-21647 actively exploited?

    No — CVE-2025-21647 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

  • What is Out-of-bounds Read (CWE-125)?

    The product reads data past the end or before the beginning of the intended buffer. View CWE-125 on MITRE CWE →

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