CVE-2026-72199 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
ntfs: validate resident index root values on lookup
Resident $INDEX_ROOT values carry index header fields that callers consume after lookup. Some callers already validate parts of the layout before walking entries, but those checks are scattered and do not cover all root header invariants, such as entries_offset alignment and lower bound, index_length, and allocated_size consistency.
The resident root resize paths now keep these header fields consistent while the value size changes: ntfs_ir_truncate() lowers index.allocated_size before shrinking the resident value, and ntfs_ir_reparent() grows the resident value before publishing a larger root header. Lookup-time validation can therefore cover these invariants without tripping over the driver's own resize paths.
Add $INDEX_ROOT to the minimum resident value size table and validate the resident index header fields before returning the attribute from lookup. Require 8-byte aligned index header fields, a sane entries_offset, an index_length within allocated_size, allocated_size within the resident value, and enough entry space for at least an index entry header.
The shared validator already rejects non-resident records for resident-only attribute types, including $INDEX_ROOT.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability in question affects the ntfs driver within the Linux kernel, specifically concerning the validation of resident index root values during lookup operations. This issue stems from inadequate validation of index header fields that are consumed by callers after lookup procedures complete. The problem manifests when resident $INDEX_ROOT attributes contain header fields that must be consistent and properly aligned, but existing validation mechanisms were fragmented and incomplete. These scattered checks failed to address critical header invariants including entries_offset alignment requirements, lower bound constraints, index_length boundaries, and consistency between allocated_size and actual data structure dimensions. Without comprehensive validation, malicious or malformed data could potentially exploit these inconsistencies to cause unexpected behavior or system instability.
The technical flaw involves the manipulation of resident index root structures during resize operations without maintaining header field consistency throughout the process. The ntfs_ir_truncate() function was responsible for lowering index.allocated_size before shrinking the resident value, while ntfs_ir_reparent() grew the resident value before publishing a larger root header. This sequence created potential inconsistencies where validation performed at lookup time could encounter malformed header fields that were temporarily inconsistent due to the driver's own resize operations. The vulnerability essentially allowed for a race condition or state inconsistency between the internal resize logic and the external validation routines, creating an attack surface where malformed index header data could be processed without proper verification.
Operationally, this vulnerability could enable attackers to manipulate ntfs filesystem structures in ways that might lead to denial of service conditions, data corruption, or potentially privilege escalation within the kernel context. The improper validation of resident index root values means that corrupted or maliciously crafted filesystem metadata could cause kernel crashes during lookup operations or allow for unexpected behavior when traversing directory structures. The impact extends beyond simple filesystem access as it affects the core kernel driver functionality that handles ntfs filesystem parsing and navigation, potentially affecting systems running ntfs filesystems with elevated privileges.
The resolution addresses this vulnerability by implementing comprehensive validation of resident index header fields before returning attributes from lookup operations. The fix requires 8-byte alignment for index header fields and establishes sanity checks for entries_offset values, ensures index_length remains within allocated_size boundaries, verifies that allocated_size fits within the resident value dimensions, and confirms sufficient entry space exists for at least an index entry header. Additionally, the solution adds $INDEX_ROOT to the minimum resident value size table to ensure proper sizing constraints are maintained throughout the filesystem structure. This approach aligns with common security practices for kernel-level input validation and follows established principles of defensive programming that prevent malformed data from propagating through system calls.
The fix demonstrates adherence to security best practices by implementing centralized validation logic rather than scattered checks, reducing the attack surface and ensuring all header invariants are consistently enforced. This type of vulnerability would typically map to CWE-129 or CWE-787 depending on specific exploitation vectors, and could potentially be leveraged as part of broader attacks within the ATT&CK framework under the techniques related to privilege escalation and kernel exploitation. The solution represents a defensive programming approach that enhances the robustness of filesystem drivers against malformed input data, which is particularly important for storage subsystems that handle untrusted data from external sources.
The implementation ensures that shared validation routines properly reject non-resident records for resident-only attribute types while maintaining compatibility with existing filesystem operations. This approach prevents the exploitation of inconsistencies between internal driver state management and external validation checks, establishing a more secure foundation for ntfs filesystem handling within the Linux kernel ecosystem. The fix essentially creates a more robust validation pipeline that prevents malformed index root structures from being processed, thereby protecting the system against potential kernel-level instabilities or security breaches originating from ntfs filesystem corruption or malicious manipulation.