What is CVE-2025-21836?

CVE-2025-21836 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10, affecting Linux kernel versions from 5.19 onward and patched in 6.6.79, 6.12.16, 6.13.4 and others. CVE-2025-21836 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

What is the CVSS score for CVE-2025-21836?

CVE-2025-21836 has a CVSS score of 5.5 out of 10, rated Medium severity. The vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

Is there a patch available for CVE-2025-21836?

Yes, CVE-2025-21836 has been patched. Fixed versions include 6.6.79, 6.12.16, 6.13.4 and others. If you are running Linux kernel 5.19 or later up to the fix versions, apply the relevant patch for your kernel branch.

Is CVE-2025-21836 actively exploited?

CVE-2025-21836 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

CVE-2025-21836

Medium

In the Linux kernel, the following vulnerability has been resolved: io_uring/kbuf: reallocate buf lists on upgrade IORING_REGISTER_PBUF_RING can reuse an old struct io_buffer_list if it was created for legacy selected buffer and has been emptied. It violates the requirement that most of the field should stay stable after publish. Always reallocate it instead.

Package Linux Kernel

Published 2025-03-07

Last modified 2026-03-07

CVSS version 3.1

Patch available

Yes

CVSS 3.1 score

5.5

out of 10

Medium

Attack Vector

Local

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

High

Vector string

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

Affected versions

Linux kernel versions 5.19 and later are affected. Fixed in 6.6.79, 6.12.16, 6.13.4, 6.14 and their respective stable series.

Affected from

≥ 5.19

Fixed in

✓ 6.6.79 6.6.x ✓ 6.12.16 6.12.x ✓ 6.13.4 6.13.x ✓ 6.14

References

The following references provide additional information about CVE-2025-21836 including vendor advisories, patch commits, exploit details, and third-party analysis. Links are sourced from the NIST NVD database.

U1F383
https://u1f383.github.io/slides/talks/2025_Hexacon-Deja_Vu_in_Linux_io_uring_Breaking_Memory_Sharing_Again_After_Generations_of_Fixes.pdf
Kernel patch commit
https://git.kernel.org/stable/c/146a185f6c05ee263db715f860620606303c4633
Patch
Kernel patch commit
https://git.kernel.org/stable/c/2a5febbef40ce968e295a7aeaa5d5cbd9e3e5ad4
Patch
Kernel patch commit
https://git.kernel.org/stable/c/7d0dc28dae836caf7645fef62a10befc624dd17b
Patch

4 patch commits total View all on NVD

Details

CVE ID CVE-2025-21836

Severity Medium

CVSS score 5.5 / 10

CVSS version 3.1

Published 2025-03-07

Modified 2026-03-07

KEV No

Patch

Yes

Package linux

Frequently asked questions

What is CVE-2025-21836?

CVE-2025-21836 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10 . It affects Linux kernel versions from 5.19 onward and has been patched in 6.6.79, 6.12.16, 6.13.4 and others. CVE-2025-21836 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.
What is the CVSS score for CVE-2025-21836?

CVE-2025-21836 has a CVSS score of 5.5 out of 10, rated Medium severity (CVSS 3.1). The vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.
Is there a patch available for CVE-2025-21836?

Yes — CVE-2025-21836 has been patched. Fixed versions include 6.6.79, 6.12.16, 6.13.4 and others. If you are running Linux kernel 5.19 or later up to the fix versions, apply the relevant patch for your kernel branch.
Is CVE-2025-21836 actively exploited?

No — CVE-2025-21836 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.