CVE-2026-99086 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
dm-integrity: validate the superblock on resume
dm_integrity_resume() re-reads the superblock from the device so that it picks up the flags and the recalculate position. It performs no validation on the result, while the constructor validates the superblock it reads and sizes all the in-memory structures according to it. The user may modify the superblock on the underlying device while the dm-integrity device is suspended, so that the two no longer agree.
In particular, access_journal_data() shifts the journal entry index by ic->sb->log2_sectors_per_block, while ic->journal_section_sectors and the journal page list were computed with the value that was present at constructor time. Increasing log2_sectors_per_block makes the index run past the end of the journal, and dm-integrity then writes 512 bytes through lowmem_page_address(NULL).
Snapshot the validated superblock in the constructor and refuse to resume if any of the fields that describe the on-disk geometry changed.
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Analysis
by VulDB Data Team • 10/24/2026
The Linux kernel device-mapper integrity target contains a critical logic flaw within its resume mechanism, specifically affecting how it handles state restoration after suspension. The dm_integrity_resume function is designed to re-read the superblock from the underlying block device to retrieve current flags and recalculate positions necessary for operation. However, this process lacks any validation of the retrieved data against previously established parameters. In contrast, the constructor phase performs rigorous validation of the superblock before sizing all in-memory structures based on its contents. This discrepancy creates a dangerous state where the kernel's internal representation can diverge from the actual disk geometry if an attacker or malicious user modifies the superblock while the device is suspended.
This lack of consistency checking leads to severe memory corruption vulnerabilities during resume operations. Specifically, the access_journal_data function relies on the log2_sectors_per_block field within the superblock to shift journal entry indices. If this value has been altered from its original state recorded at construction time, the calculated index can exceed the bounds of the allocated journal structures. Consequently, dm-integrity attempts to write fifty-one-two bytes through a null pointer via lowmem_page_address(NULL). This results in arbitrary memory writes or kernel panics, effectively allowing local privilege escalation if an unprivileged user has access to suspend and resume device-mapper devices, or potentially remote exploitation if the underlying storage is network-attached and susceptible to tampering during suspension windows.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the system fails to adequately verify that the resumed superblock matches expected constraints before proceeding with operations based on it. It also relates to CWE-787 Out-of-bounds Write due to the memory corruption resulting from invalid index calculations. In terms of attack vectors, this falls under ATT&CK technique T1059 Command and Scripting Interpreter if exploited via scriptable interfaces that control device-mapper states, or more broadly as a Local Privilege Escalation path where an attacker manipulates block device metadata to trigger kernel code execution with elevated privileges.
The resolution involves snapshotting the validated superblock during the initial constructor phase and enforcing strict consistency checks upon resume. The system must refuse to resume if any fields describing on-disk geometry, such as log2_sectors_per_block, have changed since initialization. This ensures that the in-memory structures remain aligned with the actual disk layout, preventing out-of-bounds accesses. Administrators should ensure their systems are updated with patches addressing this dm-integrity flaw and restrict access to device-mapper management tools to trusted users only until updates are applied. Regular auditing of block device configurations can also help detect unauthorized modifications that might precede such exploitation attempts.