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Linux KernelOperating system · Linux

CVE-2025-21993

HIGH · 7.1 CVSS v3.1 Published 2025-04-02
Fix available
A fix is available. Upgrade to 6.1.132 / 6.6.84 or later.
See remediation →
73/100
Remediation priority · Elevated
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: iscsi_ibft: Fix UBSAN shift-out-of-bounds warning in ibft_attr_show_nic() When performing an iSCSI boot using IPv6, iscsistart still reads the /sys/firmware/ibft/ethernetX/subnet-mask entry. Since the IPv6 prefix length is 64, this causes the shift exponent to become negative, triggering a UBSAN warning. As the concept of a subnet mask does not apply to IPv6, the value is set to ~0 to suppress the warning message.

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-125

The code reads past the end (or before the start) of a buffer, returning memory that was never meant to be exposed. Attackers use it to leak secrets like keys or to defeat memory-protection defences. Remediation is validating indices and lengths before every read.

General guidance for the out-of-bounds read 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:< 6.1.132>= 6.2, < 6.6.84>= 6.7, < 6.12.20>= 6.13, < 6.13.8= 6.14

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
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/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 6.1.132 / 6.6.84 / 6.12.20 or later
Fixed in 6.1.1326.6.846.12.20
Vendor patch git.kernel.org →
Recommended fix High confidence

Upgrade to kernel 6.1.132+, 6.6.84+, 6.12.20+, or 6.13.8+ depending on your current branch

  1. 1. Identify the currently running Linux kernel version using 'uname -r'
  2. 2. Determine which major kernel branch you are on (e.g., 6.1.x, 6.2-6.6.x, 6.7-6.12.x, or 6.13.x)
  3. 3. Upgrade to a kernel version that includes the fix: For 6.1.x upgrade to >=6.1.132; For 6.2-6.6.x upgrade to >=6.6.84; For 6.7-6.12.x upgrade to >=6.12.20; For 6.13.x upgrade to >=6.13.8
  4. 4. Update bootloader configuration if necessary (e.g., update-grub for GRUB)
  5. 5. Reboot the system into the new kernel
  6. 6. Verify the fix is applied by checking the kernel version matches the fixed release and by confirming the UBSAN warning no longer appears in kernel logs (dmesg | grep -i ubsan)
Caveat Kernel upgrades may introduce compatibility changes with custom modules or specific hardware drivers; ensure driver compatibility before upgrading

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-2025-21993 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data