CVE-2026-90203

A flaw was found in Squashfs, a compressed read-only filesystem within the Linux kernel. A local attacker with administrative privileges could create a specially crafted Squashfs filesystem that contains a negative block offset. If this malicious filesystem is mounted, an unprivileged user could then read a crafted file within it, leading to an out-of-bounds memory access. This vulnerability could result in information disclosure or a denial of service.

A Squashfs image can encode a negative block offset that reaches squashfs_copy_data during file reads. The missing negative offset check can make the kernel read before the decompressed fragment buffer and copy out-of-bounds data into the file read path, which may expose adjacent kernel memory and may also crash the system. For the CVSS the PR:N is used in the paranoid user-assisted scenario where an attacker supplied filesystem image is mounted by an administrator or automount flow, and the attacker only needs access to read the crafted file after mount. Direct mounting of the crafted image normally requires CAP_SYS_ADMIN, so the base score uses PR:H. The issue is local and is not network reachable by itself. Impact is primarily confidentiality loss from an out-of-bounds read, with possible denial of service if the invalid access crashes the kernel.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.