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Linux KernelOperating system · Linux

CVE-2025-38415

HIGH · 7.8 CVSS v3.1 Published 2025-07-25
Fix available
A fix is available. Upgrade to 5.4.295 / 5.10.239 or later.
See remediation →
80/100
Remediation priority · High
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: Squashfs: check return result of sb_min_blocksize Syzkaller reports an "UBSAN: shift-out-of-bounds in squashfs_bio_read" bug. Syzkaller forks multiple processes which after mounting the Squashfs filesystem, issues an ioctl("/dev/loop0", LOOP_SET_BLOCK_SIZE, 0x8000). Now if this ioctl occurs at the same time another process is in the process of mounting a Squashfs filesystem on /dev/loop0, the failure occurs. When this happens the following code in squashfs_fill_super() fails. ---- msblk->devblksize = sb_min_blocksize(sb, SQUASHFS_DEVBLK_SIZE); msblk->devblksize_log2 = ffz(~msblk->devblksize); ---- sb_min_blocksize() returns 0, which means msblk->devblksize is set to 0. As a result, ffz(~msblk->devblksize) returns 64, and msblk->devblksize_log2 is set to 64. This subsequently causes the UBSAN: shift-out-of-bounds in fs/squashfs/block.c:195:36 shift exponent 64 is too large for 64-bit type 'u64' (aka 'unsigned long long') This commit adds a check for a 0 return by sb_min_blocksize().

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-787

The program writes past the bounds of a buffer, overwriting adjacent memory an attacker can turn to their advantage. Crafted input can overwrite control data and redirect execution. Remediation is validating every index and length before a write, plus modern memory-safety mitigations.

General guidance for the out-of-bounds write 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:>= 2.6.29, < 5.4.295>= 5.5, < 5.10.239>= 5.11, < 5.15.186>= 5.16, < 6.1.142>= 6.2, < 6.6.94>= 6.7, < 6.12.34>= 6.13, < 6.15.3
Debian LinuxOperating system
Affected:= 11.0

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
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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 5.4.295 / 5.10.239 / 5.15.186 or later
Fixed in 5.4.2955.10.2395.15.186
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux Kernel 6.1.142+ (or 5.15.186+, 5.10.239+, 5.4.295+ depending on branch)

  1. 1. Identify the currently running kernel version using 'uname -r'
  2. 2. Check if the running kernel version is affected (< 5.4.295, < 5.10.239, < 5.15.186, or < 6.1.142)
  3. 3. Upgrade to a fixed kernel version: for 6.1.y LTS branch upgrade to >= 6.1.142, or for other affected branches upgrade to the corresponding fixed version (5.4.295, 5.10.239, or 5.15.186)
  4. 4. Reboot the system to load the fixed kernel
  5. 5. Verify the fix is applied by checking the kernel version and confirming the sb_min_blocksize check exists in the source (if building custom kernel)
Caveat Kernel upgrades may require system reboot and could have compatibility implications with custom modules or specific hardware drivers; ensure backup and test in non-production environment first

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-2025-38415 in production — separate from our analysis above.

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What this is

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