CVE-2025-40049 Squashfs: fix uninit-value in squashfs_get_parent
A local attacker can trigger an uninitialized value access in the Squashfs filesystem, potentially leaking kernel memory information.
- 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-2025-40049?
CVE-2025-40049 is a vulnerability in Linux, published on 28 Oct 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: fix uninit-value in squashfs_get_parent
Syzkaller reports a "KMSAN: uninit-value in squashfs_get_parent" bug.
This is caused by open_by_handle_at() being called with a file handle containing an invalid parent inode number. In particular the inode number is that of a symbolic link, rather than a directory.
Squashfs_get_parent() gets called with that symbolic link inode, and accesses the parent member field.
unsigned int parent_ino = squashfs_i(inode)->parent;
Because non-directory inodes in Squashfs do not have a parent value, this is uninitialised, and this causes an uninitialised value access.
The fix is to initialise parent with the invalid inode 0, which will cause an EINVAL error to be returned.
Regular inodes used to share the parent field with the block_list_start field. This is removed in this commit to enable the parent field to contain the invalid inode number 0.
Which versions are affected by CVE-2025-40049?
How do I fix CVE-2025-40049?
Apply the vendor's patch.
Is CVE-2025-40049 being exploited?
There is no known exploitation of CVE-2025-40049 in the wild and no public exploit code.
Sources
Also known as AZL-68915, BELL-CVE-2025-40049, DEBIAN-CVE-2025-40049, GHSA-pq9p-38r9-fjq5, ROOT-OS-DEBIAN-11-CVE-2025-40049, ROOT-OS-UBUNTU-2204-CVE-2025-40049 and 2 more.