CVE-2026-98636 squashfs: Add dictionary size range check to prevent shift-out-of-bounds

Q: Is CVE-2026-98636 being exploited?

There is no known exploitation of CVE-2026-98636 in the wild and no public exploit code.

Not scored Published 18 Oct 2026 Updated 19 Oct 2026

A local attacker can cause a denial of service by mounting a malicious SquashFS image that triggers a shift-out-of-bounds error in the Linux kernel.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Local or same network only
Victim action needed: A user has to click or open something
Fix: Available

What is CVE-2026-98636?

CVE-2026-98636 is a vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

Official description

In the Linux kernel, the following vulnerability has been resolved:

squashfs: Add dictionary size range check to prevent shift-out-of-bounds

When an abnormal SquashFS image (COMP_OPTS flag is 1 but dictionary size is 0) is mounted, and performs shift operations using dictionarysize, the shift exponent is -1, causing a shift-out-of-bounds.

Detail as below: squashfs_comp_opts(msblk, buffer, length) squashfs_xz_comp_opts() if (comp_opts) n = ffs(opts->dict_size) - 1;<----opts->dict_size=0, n=-1 if (opts->dict_size != (1 << n) && opts->dict_size != (1 << n) + (1 << (n + 1))) <----shift-out-of-bounds

Fix it by adding a dictionary size range check before the shift operation.

Which versions are affected by CVE-2026-98636?

How do I fix CVE-2026-98636?

Apply the vendor's patch.

Is CVE-2026-98636 being exploited?