CVE-2026-90161 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
erofs: fix interlaced ztailpacking pclusters
On-disk sizes of interlaced pclusters should be block-aligned, and ztailpacking interlaced pclusters should be invalid at all.
Currently, mkfs.erofs won't generate any interlaced pcluster with ztailpacking enabled, so this doesn't affect any existing valid filesystems.
However, crafted images can contain invalid interlaced ztailpacking pclusters, resulting in an out-of-bounds read from a kmap'd page and copying irrelevant kernel memory into userspace-visible page cache.
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Analysis
by VulDB Data Team • 09/17/2026
The Extensible File System (EROFS) is a high-performance, decompression-only file system designed for embedded systems and Android devices within the Linux kernel ecosystem. A critical vulnerability has been identified in the handling of interlaced pclusters when ztailpacking features are enabled. This flaw stems from an insufficient validation mechanism during the processing of on-disk data structures, specifically regarding how block alignment is enforced for interlaced physical clusters. The core technical deficiency lies in the kernel's failure to strictly validate that the on-disk sizes of these specific cluster types adhere to mandatory block-alignment constraints. Furthermore, the implementation incorrectly permits or fails to explicitly reject ztailpacking configurations when applied to interlaced pclusters, a combination that is fundamentally invalid according to the file system specification and design intent.
The operational impact of this vulnerability is severe due to its potential for remote exploitation via crafted disk images. Although standard tools like mkfs.erofs do not generate such malformed structures in normal operation, an attacker can construct malicious EROFS image files containing these invalid interlaced ztailpacking pclusters. When a system mounts or accesses such a crafted file system, the kernel attempts to process the corrupted metadata. This leads to an out-of-bounds read from a page that has been mapped into kernel space via kmap. The vulnerability allows for the copying of irrelevant and potentially sensitive kernel memory data directly into userspace-visible page cache structures. Consequently, this results in an information disclosure vulnerability where arbitrary kernel memory contents can be leaked to unprivileged user-space applications.
From a classification perspective, this issue aligns with CWE-125, which describes Out-of-bounds Read vulnerabilities. The lack of proper boundary checks when processing the size and alignment parameters of interlaced pclusters permits access beyond the allocated buffer limits. Additionally, because the vulnerability involves reading kernel memory that is not intended for user consumption, it also relates to CWE-200, Exposure of Sensitive Information to an Unauthorized Actor. In terms of attack vectors, this falls under ATT&CK technique T1530, Data from Local System, specifically involving data staging or exfiltration through file system metadata parsing mechanisms rather than direct code execution.
Mitigation strategies for this vulnerability primarily involve applying the upstream kernel patches that enforce strict validation rules on pcluster sizes and explicitly invalidate ztailpacking configurations for interlaced clusters. Administrators should ensure their systems are updated to a version of the Linux kernel where these EROFS fixes have been integrated. For environments relying on custom or third-party generated file system images, rigorous integrity checking and validation tools must be employed before mounting any external storage media formatted with EROFS. Additionally, enabling strict memory protection features such as Kernel Page Table Isolation (KPTI) can help mitigate the impact of information disclosure by isolating kernel addresses from user space, although patching remains the definitive solution to eliminate the root cause in the file system driver logic.