CVE-2026-97437 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
ntfs3: fix out-of-bounds read in ntfs_dir_emit() and hdr_find_e()
The bounds check in ntfs_dir_emit() compares fname->name_len (a character count) against e->size (a byte count) without accounting for the 2-byte-per-character UTF-16LE encoding or the ATTR_FILE_NAME header size:
if (fname->name_len + sizeof(struct NTFS_DE) > le16_to_cpu(e->size))
This computes: name_len + 16 > e_size
The correct check must account for the ATTR_FILE_NAME header (66 bytes before the name) and the UTF-16LE character size (2 bytes each):
sizeof(NTFS_DE) + offsetof(ATTR_FILE_NAME, name) + name_len * sizeof(short) > e_size
Which computes: 16 + 66 + name_len * 2 > e_size
The correct calculation already exists as fname_full_size() in ntfs.h and is used in cmp_fnames(), namei.c, and fslog.c, but was not used in the readdir path.
A crafted NTFS image with an index entry containing a small e->size but large fname->name_len bypasses the current check, causing ntfs_utf16_to_nls() to read past the entry boundary.
Additionally, add a key_size validation in hdr_find_e() to ensure the declared key_size does not exceed the available entry data, preventing comparison functions from reading past entry boundaries on the lookup path.
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Analysis
by VulDB Data Team • 09/24/2026
The Linux kernel's ntfs3 filesystem driver contains a critical out-of-bounds read vulnerability within its directory handling logic, specifically affecting the ntfs_dir_emit and hdr_find_e functions. This flaw stems from an incorrect implementation of bounds checking when processing NTFS index entries that contain file name attributes. The underlying technical issue arises because the existing validation code fails to account for two fundamental aspects of the NTFS data structure: the byte-based nature of attribute sizes versus character counts, and the specific header overhead associated with ATTR_FILE_NAME structures. By treating a filename length as if it were directly comparable to raw buffer sizes without conversion or offset adjustments, the kernel allows crafted inputs to bypass safety checks, leading to memory corruption risks through excessive reads beyond allocated entry boundaries.
The core of the vulnerability lies in the ntfs_dir_emit function, which is responsible for emitting directory entries during readdir operations. The flawed logic compares fname->name_len against e->size using a simple addition that includes only the size of the NTFS_DE structure, calculated as name_len plus sixteen bytes. This approach erroneously assumes that the filename length represents byte counts and ignores the substantial header overhead preceding the actual filename data within an ATTR_FILE_NAME attribute. In reality, filenames in this context are encoded in UTF-16LE, meaning each character occupies two bytes rather than one. Furthermore, there is a fixed sixty-six-byte header associated with the ATTR_FILE_NAME structure that must be included before any name data begins. Consequently, the correct boundary check should verify whether sixteen plus sixty-six plus twice the filename length exceeds the total entry size. The kernel already possesses a helper function named fname_full_size in ntfs.h that correctly calculates this value and is utilized elsewhere for comparison operations, but it was inadvertently omitted from the readdir path where this vulnerability manifests.
This oversight enables an attacker to craft a malicious NTFS image containing index entries with deceptively small declared sizes paired with large filename lengths. When such a crafted entry is processed by ntfs_dir_emit, the insufficient bounds check allows the subsequent call to ntfs_utf16_to_nls to read past the end of the allocated memory region for that entry. This out-of-bounds read can potentially expose sensitive kernel memory contents or lead to unpredictable system behavior depending on what data resides immediately after the buffer boundary. The vulnerability is classified under CWE-125, which describes Out-of-Bounds Read vulnerabilities where software reads data past the end of a buffer. From an offensive security perspective, this aligns with ATT&CK techniques related to unauthorized access to memory or information discovery through exploitation of filesystem parsing errors.
A secondary but related issue exists within the hdr_find_e function used during lookup operations. This function also lacks adequate validation for key sizes declared in index entries. Without proper verification that the declared key_size does not exceed the available entry data, comparison functions invoked by this routine may attempt to read beyond valid boundaries when resolving file lookups. While potentially less immediately exploitable than the readdir path due to different access patterns, it still represents a significant integrity risk within the filesystem driver's core lookup mechanisms. Both issues highlight a systemic failure in enforcing strict adherence to NTFS structural constraints during parsing operations.
Mitigation for this vulnerability requires applying kernel updates that patch both ntfs_dir_emit and hdr_find_e with corrected bounds checking logic. Developers must ensure that all filename length comparisons utilize the existing fname_full_size helper or equivalent calculations that properly account for UTF-16LE encoding multipliers and ATTR_FILE_NAME header offsets. System administrators should prioritize updating their Linux kernels to versions containing these fixes, particularly on systems mounting untrusted or externally sourced NTFS volumes. Additionally, implementing strict input validation at mount time or using filesystem monitoring tools can help detect attempts to exploit malformed index entries before they trigger the vulnerable code paths.