CVE-2025-38415: debian linux Memory Corruption — Fix

Description

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().

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CVSS v3.1 Score

7.8

HIGH

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

Weakness Type (CWE)

CWE-787 Out-of-bounds Write

Affected Products

Vendor	Product	Versions
linux	linux_kernel	2.6.29 — 5.4.295
linux	linux_kernel	5.5 — 5.10.239
linux	linux_kernel	5.11 — 5.15.186
linux	linux_kernel	5.16 — 6.1.142
linux	linux_kernel	6.2 — 6.6.94
linux	linux_kernel	6.7 — 6.12.34
linux	linux_kernel	6.13 — 6.15.3
debian	debian_linux	All

References

Advisories & Patches

https://git.kernel.org/stable/c/0aff95d9bc7fb5400ca8af507429c4b067bdb425 https://git.kernel.org/stable/c/295ab18c2dbce8d0ac6ecf7c5187e16e1ac8b282 https://git.kernel.org/stable/c/4f99357dadbf9c979ad737156ad4c37fadf7c56b https://git.kernel.org/stable/c/549f9e3d7b60d53808c98b9fde49b4f46d0524a5 https://git.kernel.org/stable/c/5c51aa862cbeed2f3887f0382a2708956710bd68 https://git.kernel.org/stable/c/6abf6b78c6fb112eee495f5636ffcc350dd2ce25 https://git.kernel.org/stable/c/734aa85390ea693bb7eaf2240623d41b03705c84 https://git.kernel.org/stable/c/db7096ea160e40d78c67fce52e7cc51bde049497

Other References

https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html

Frequently Asked Questions

What is CVE-2025-38415? +

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(). It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2025-38415? +

CVE-2025-38415 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2025-38415? +

CVE-2025-38415 affects products from debian, linux, specifically: debian_linux, linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-38415? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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