CVE-2025-21643

Medium

In the Linux kernel, the following vulnerability has been resolved: netfs: Fix kernel async DIO Netfslib needs to be able to handle kernel-initiated asynchronous DIO that is supplied with a bio_vec[] array. Currently, because of the async flag, this gets passed to netfs_extract_user_iter() which throws a warning and fails because it only handles IOVEC and UBUF iterators. This can be triggered through a combination of cifs and a loopback blockdev with something like: mount //my/cifs/share /foo dd if=/dev/zero of=/foo/m0 bs=4K count=1K losetup --sector-size 4096 --direct-io=on /dev/loop2046 /foo/m0 echo hello >/dev/loop2046 This causes the following to appear in syslog: WARNING: CPU: 2 PID: 109 at fs/netfs/iterator.c:50 netfs_extract_user_iter+0x170/0x250 [netfs] and the write to fail. Fix this by removing the check in netfs_unbuffered_write_iter_locked() that causes async kernel DIO writes to be handled as userspace writes. Note that this change relies on the kernel caller maintaining the existence of the bio_vec array (or kvec[] or folio_queue) until the op is complete.

Package Linux Kernel
Published 2025-01-19
Last modified 2025-10-16
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 6.8 and later are affected. Fixed in 6.12.10, 6.13 and their respective stable series.

Affected from
≥ 6.8
Fixed in
✓ 6.12.10 6.12.x ✓ 6.13

References

The following references provide additional information about CVE-2025-21643 including vendor advisories, patch commits, exploit details, and third-party analysis. Links are sourced from the NIST NVD database.

Frequently asked questions

  • What is CVE-2025-21643?

    CVE-2025-21643 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10 . It affects Linux kernel versions from 6.8 onward and has been patched in 6.12.10 and 6.13. CVE-2025-21643 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2025-21643?

    CVE-2025-21643 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-2025-21643?

    Yes — CVE-2025-21643 has been patched. Fixed versions include 6.12.10 and 6.13. If you are running Linux kernel 6.8 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2025-21643 actively exploited?

    No — CVE-2025-21643 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

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