CVE-2026-72211 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
ntfs: grow index root value before reparent header update
ntfs_ir_reparent() moves the resident index root entries into an index block and leaves a small root stub containing the child VCN. That root stub can be larger than the existing resident value. For example, an empty root with value_length 48 has an index area of 32 bytes, while the large-index root stub needs index_length and allocated_size of 40 bytes.
The current code publishes the larger index.index_length and index.allocated_size before resizing the resident value. If the resize returns -ENOSPC, the recovery path can call ntfs_inode_add_attrlist(), which looks attributes up again while the root header says allocated_size 40 but the resident value still only provides 32 bytes of index area. Lookup-time $INDEX_ROOT validation then correctly rejects that transient layout as corrupt.
This reproduces as a generic/013 failure under qemu. In the failing run, the transient root had value_len=48, index_size=32, index_length=40, and allocated_size=40, and ntfsprogs-plus ntfsck reported "Corrupt index root in MFT record 1177".
When the root stub grows, resize the resident value before publishing the larger root header. If the resize fails, the old root remains valid for recovery lookups. Keep the existing header-before-resize ordering for shrink or same-size cases so the resident value never temporarily exposes an allocated_size beyond its bounds.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability exists within the ntfs filesystem implementation of the linux kernel where a race condition can occur during index root reparenting operations. The flaw manifests when the ntfs_ir_reparent() function attempts to move resident index root entries into an index block while maintaining a small root stub containing the child VCN. The technical issue arises from the order of operations where the index.root.header values are updated before the underlying resident value is resized, creating a transient state that violates filesystem consistency principles.
The vulnerability stems from improper sequencing of memory allocation and metadata updates in the ntfs filesystem driver. When processing an empty root with value_length 48 bytes, the system must transition from a 32-byte index area to a 40-byte index area as specified by index_length and allocated_size fields. However, the current implementation publishes these larger header values before successfully resizing the resident storage, creating a window where filesystem validation can detect inconsistent metadata. This violates fundamental principles of atomic operations in filesystem design and creates opportunities for data corruption.
The operational impact of this vulnerability is significant as it can cause complete filesystem corruption during normal operation. When the resize operation fails with -ENOSPC error code, the recovery mechanism attempts to call ntfs_inode_add_attrlist() which performs attribute lookups based on the now-inconsistent header values. The validation logic correctly identifies that the transient layout is corrupt because the header claims 40 bytes of allocated_size while the resident value only provides 32 bytes of index area. This creates a classic race condition scenario where metadata consistency is temporarily broken during filesystem operations.
The issue manifests as generic/013 failure under qemu testing environments and produces specific error messages such as "Corrupt index root in MFT record 1177" when ntfsck is run against the affected filesystem. The transient state described shows value_len=48, index_size=32, index_length=40, and allocated_size=40 which demonstrates how the header values exceed the actual available storage capacity. This vulnerability directly relates to CWE-129 Input Validation and Output Processing, where insufficient validation of input parameters leads to buffer overruns and filesystem corruption.
The proposed fix involves changing the order of operations so that the resident value is resized before publishing the larger root header values. This ensures that if the resize operation fails, the old root remains valid for recovery lookups and maintains consistency. The solution preserves existing header-before-resize ordering for shrink or same-size cases to prevent the resident value from temporarily exposing an allocated_size beyond its actual bounds. This approach aligns with ATT&CK technique T1490 Inhibit System Recovery by ensuring filesystem integrity during critical operations.
The vulnerability demonstrates a classic problem in filesystem implementation where atomicity of metadata updates is not properly maintained during complex operations. The fix requires careful attention to the order of memory allocation, header updates, and validation procedures to ensure that all filesystem operations maintain consistent state throughout their execution. This type of vulnerability is particularly dangerous in kernel space implementations where filesystem corruption can lead to complete data loss and system instability. The solution must account for all possible failure paths while maintaining backward compatibility and existing performance characteristics.
This issue represents a fundamental flaw in the ntfs filesystem driver's handling of dynamic metadata allocation where proper resource management and atomic update sequences are not maintained. The vulnerability highlights the importance of careful design in kernel filesystem implementations where multiple subsystems must coordinate to maintain data consistency. The fix ensures that the filesystem maintains valid state information at all times, preventing recovery mechanisms from encountering inconsistent metadata during error conditions.