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Linux Kernel CVE-2025-38415

HIGH
Out-of-bounds Write (CWE-787)
2025-07-25 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Buffer Overflow Linux Memory Corruption Debian Red Hat Debian Linux Suse
7.8
CVSS 3.1 · NVD
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Severity by source

NVD PRIMARY
7.8 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
5.8 MEDIUM

Local race condition needing concurrent mount and loop ioctl makes AC:H; PR:L assumes unprivileged user namespaces; demonstrated impact is mainly DoS with possible memory corruption, so A:H but C/I downgraded to L.

3.1 AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
4.0 AV:L/AC:H/AT:N/PR:L/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
SUSE
5.8 MEDIUM
AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
Red Hat
7.1 MEDIUM
qualitative

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

2
Analysis Generated
Jun 18, 2026 - 22:00 vuln.today
CVE Published
Jul 25, 2025 - 14:15 nvd
HIGH 7.8

DescriptionNVD

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().

AnalysisAI

Out-of-bounds shift in the Linux kernel Squashfs filesystem allows a local attacker to trigger memory corruption by racing a LOOP_SET_BLOCK_SIZE ioctl against a concurrent Squashfs mount on the same loop device, causing sb_min_blocksize() to return 0 and the code in squashfs_fill_super() to compute a shift exponent of 64. The affected subsystem is the kernel Squashfs driver (fs/squashfs/block.c) on Linux and downstream distributions such as Debian 11. There is no public exploit identified at time of analysis and the issue is not listed in CISA KEV.

Technical ContextAI

The bug lives in the Squashfs read-only filesystem driver. During mount, squashfs_fill_super() calls sb_min_blocksize() to negotiate the device block size, then computes devblksize_log2 via ffz(~devblksize). If a parallel ioctl(LOOP_SET_BLOCK_SIZE) on the backing /dev/loop device changes block size mid-mount, sb_min_blocksize() can return 0; ffz(~0) then returns 64, which is later used as a shift exponent against a 64-bit type in fs/squashfs/block.c:195, producing undefined behavior caught by UBSAN. Root cause is CWE-787 (out-of-bounds write) stemming from an unchecked return value, exposed by the absence of synchronization between loop-device block-size changes and filesystem superblock initialization. The bug was discovered by Syzkaller fuzzing the Squashfs/loop interaction.

RemediationAI

Apply the upstream fix available per vendor advisory by updating to a Linux kernel that includes one of the stable commits 0aff95d9bc7fb5400ca8af507429c4b067bdb425, 295ab18c2dbce8d0ac6ecf7c5187e16e1ac8b282, 4f99357dadbf9c979ad737156ad4c37fadf7c56b, 549f9e3d7b60d53808c98b9fde49b4f46d0524a5, 5c51aa862cbeed2f3887f0382a2708956710bd68, 6abf6b78c6fb112eee495f5636ffcc350dd2ce25, 734aa85390ea693bb7eaf2240623d41b03705c84, or db7096ea160e40d78c67fce52e7cc51bde049497 - all on git.kernel.org/stable. Debian 11 users should install the LTS update per https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html and msg00008.html. As compensating controls until patched, disable unprivileged user namespaces by setting kernel.unprivileged_userns_clone=0 (sysctl) which prevents unprivileged users from triggering the mount path but breaks rootless containers like rootless Podman and unprivileged Docker; alternatively, blacklist the squashfs module via modprobe.d if Squashfs is not required (breaks live ISOs, snap packages, and some appliance images); or restrict access to /dev/loop* devices via udev rules and seccomp to deny LOOP_SET_BLOCK_SIZE for unprivileged processes (may break legitimate loopback workflows).

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
Container suse/sl-micro/6.0/base-os-container:2.1.3-7.44 Container suse/sl-micro/6.1/base-os-container:2.2.1-5.27 Image SL-Micro Image SL-Micro-Azure Image SL-Micro-BYOS-Azure Image SL-Micro-BYOS-EC2 Image SL-Micro-BYOS-GCE Image SL-Micro-EC2 Image SLE-Micro Image SLE-Micro-Azure Image SLE-Micro-BYOS Image SLE-Micro-BYOS-Azure Image SLE-Micro-BYOS-EC2 Image SLE-Micro-BYOS-GCE Image SLE-Micro-EC2 Image SLE-Micro-GCE Image SUSE-Multi-Linux-Manager-Proxy-BYOS-Azure Image SUSE-Multi-Linux-Manager-Proxy-BYOS-EC2 Image SUSE-Multi-Linux-Manager-Proxy-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-Azure-llc Image SUSE-Multi-Linux-Manager-Server-Azure-ltd Image SUSE-Multi-Linux-Manager-Server-BYOS-Azure Image SUSE-Multi-Linux-Manager-Server-BYOS-EC2 Image SUSE-Multi-Linux-Manager-Server-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-EC2-llc Image SUSE-Multi-Linux-Manager-Server-EC2-ltd Affected
Container suse/sl-micro/6.0/kvm-os-container:2.1.3-6.67 Container suse/sl-micro/6.1/kvm-os-container:2.2.1-5.29 Affected
Container suse/sl-micro/6.0/rt-os-container:2.1.3-7.76 Container suse/sl-micro/6.1/rt-os-container:2.2.1-5.14 Affected
Image SLES-Azure-3P Image SLES-Azure-Basic Image SLES-Azure-Standard Image SLES-BYOS-Azure Image SLES-BYOS-EC2 Image SLES-BYOS-GCE Image SLES-CHOST-BYOS-Aliyun Image SLES-CHOST-BYOS-Azure Image SLES-CHOST-BYOS-EC2 Image SLES-CHOST-BYOS-GCE Image SLES-CHOST-BYOS-GDC Image SLES-CHOST-BYOS-SAP-CCloud Image SLES-EC2 Image SLES-EC2-ECS Image SLES-GCE Image SLES-GCE-3P Image SLES-Hardened-BYOS-Azure Image SLES-Hardened-BYOS-EC2 Image SLES-Hardened-BYOS-GCE Image SLES-SAPCAL-Azure Image SLES-SAPCAL-EC2 Image SLES-SAPCAL-GCE Affected
Image SLES-SAP-Azure Image SLES-SAP-Azure-3P Image SLES-SAP-BYOS-Azure Image SLES-SAP-BYOS-EC2 Image SLES-SAP-BYOS-GCE Image SLES-SAP-EC2 Image SLES-SAP-GCE Image SLES-SAP-GCE-3P Affected

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CVE-2025-38415 vulnerability details – vuln.today
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