CVE-2025-38415 Squashfs: check return result of sb_min_blocksize
A race condition in the Linux kernel Squashfs driver causes an integer overflow leading to a shift-out-of-bounds error and potential denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-38415?
CVE-2025-38415 is a high-severity vulnerability in Debian Debian Linux, published on 25 Jul 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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().
Weakness: CWE-787
Which versions are affected by CVE-2025-38415?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-38415?
Apply the vendor's patch.
Is CVE-2025-38415 being exploited?
There is no known exploitation of CVE-2025-38415 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as BELL-CVE-2025-38415, DEBIAN-CVE-2025-38415, GHSA-j3rr-hppv-g55q, OESA-2025-2660, OESA-2025-2661, ROOT-OS-DEBIAN-11-CVE-2025-38415 and 4 more.