CVE-2026-31447

ext4: reject mount if bigalloc with s_first_data_block != 0

Published Apr 22, 2026 CVSS 3.1 · 7.8 High EPSS < 1% KEV · Not listed

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.

Analysis

Technical impact

In this vulnerability the Linux kernel rejects mounting an ext4 filesystem that uses the bigalloc feature while the s_first_data_block field is non-zero. This issue corresponds to CWE‑1288 (File System Format Validity Issue). The failure arises from an unchecked filesystem format condition that causes the mount operation to abort, leading to a denial of service for any process that requires access to the affected partition.

Affected Systems

The flaw impacts any Linux system that runs a kernel version that does not yet include the patch that adds the check against s_first_data_block. Administrators should consider all unpatched kernels as vulnerable, especially when ext4 filesystems are created with bigalloc enabled. The CNA vendor list shows only Linux, and no specific version ranges are provided, so all legacy kernels are potentially affected.

Risk and Exploitability

The latest CVSS score of 7.8 classifies this issue as high severity. The flaw is recognized as CWE‑1288, a file system format validity issue. Because the EPSS score is below 1%, exploitation is currently unlikely, and the vulnerability is not listed in the CISA KEV catalog. The likely attack vector is local; an attacker with root privileges or the ability to mount filesystems can trigger a denial of service by attempting to mount a bigalloc-enabled ext4 partition where s_first_data_block is non-zero. This will abort the mount operation and render the filesystem unavailable, but does not affect confidentiality or integrity.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`281b59959707dfae03ce038cdf231bf4904e170c`	affected	< 5ad6d994255e27a3254079dfb50ca861fc31f2d0
`281b59959707dfae03ce038cdf231bf4904e170c`	affected	< 3a926957cc95899ef88529710836edadc03c71a1
`281b59959707dfae03ce038cdf231bf4904e170c`	affected	< 7b58c110b4e1f028eb38eec9ed3555e9be81c8b0
`281b59959707dfae03ce038cdf231bf4904e170c`	affected	< b77de3fceafbb39f30e4ff5dc986f863d5456417
`281b59959707dfae03ce038cdf231bf4904e170c`	affected	< d787d3ae96648dc14a3b7ca8fde817177e82c1c7
`281b59959707dfae03ce038cdf231bf4904e170c`	affected	< ad1f6d608f33f59d21a3d025615d6786a6443998
`281b59959707dfae03ce038cdf231bf4904e170c`	affected	< 7d5b04290156c3fc316eecc86a4f9d201ab7d44a
`281b59959707dfae03ce038cdf231bf4904e170c`	affected	< 3822743dc20386d9897e999dbb990befa3a5b3f8

Linux

affected

Version	Status	Constraints
`3.2`	affected	—
`0`	unaffected	< 3.2
`5.10.253`	unaffected	≤ 5.10.*
`5.15.203`	unaffected	≤ 5.15.*
`6.1.168`	unaffected	≤ 6.1.*
`6.6.131`	unaffected	≤ 6.6.*
`6.12.80`	unaffected	≤ 6.12.*
`6.18.21`	unaffected	≤ 6.18.*
`6.19.11`	unaffected	≤ 6.19.*
`7.0`	unaffected	≤ *

Configuration 1 [-]

OR	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc1::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc2::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc3::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc4::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc5::::::

No data.

Vendor Product Versions

Linux

Linux Kernel

Version	Status	Scheme	Platform
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,5ad6d994255e27a3254079dfb50ca861fc31f2d0)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,3a926957cc95899ef88529710836edadc03c71a1)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,7b58c110b4e1f028eb38eec9ed3555e9be81c8b0)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,b77de3fceafbb39f30e4ff5dc986f863d5456417)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,d787d3ae96648dc14a3b7ca8fde817177e82c1c7)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,ad1f6d608f33f59d21a3d025615d6786a6443998)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,7d5b04290156c3fc316eecc86a4f9d201ab7d44a)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,3822743dc20386d9897e999dbb990befa3a5b3f8)`	affected	code_commit	—

Linux

Linux Kernel

Version	Status	Scheme	Platform
`[5.10.253,5.11.0)`	unaffected	semver	—
`[5.15.203,5.16.0)`	unaffected	semver	—
`[6.1.168,6.2.0)`	unaffected	semver	—
`[6.6.131,6.7.0)`	unaffected	semver	—
`[6.12.80,6.13.0)`	unaffected	semver	—
`[6.18.21,6.19.0)`	unaffected	semver	—
`[6.19.11,6.20.0)`	unaffected	semver	—
`[7.0,*]`	unaffected	generic	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade the kernel to a version that contains the patch that restricts bigalloc usage when s_first_data_block is non-zero.
Avoid creating ext4 filesystems with the bigalloc feature or ensure that s_first_data_block is set to zero for any required partitions; do not use bigalloc on production systems.
If an immediate kernel upgrade is not possible, reformat the affected ext4 filesystem without the bigalloc feature or remount it with corrected parameters that satisfy the kernel check.
Monitor mount attempts on the affected filesystems for failures and log such events to detect any misuse or exploitation attempts.

Generated by OpenCVE AI on October 19, 2026 at 21:29 UTC.

Tracking

Advisories

Source	ID	Title
Debian DLA	DLA-4561-1	linux-6.1 security update
Debian DLA	DLA-4606-1	linux security update
Debian DSA	DSA-6238-1	linux security update
Debian DSA	DSA-6243-1	linux security update
Ubuntu USN	USN-8567-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8574-1	Linux kernel (GCP FIPS) vulnerabilities
Ubuntu USN	USN-8575-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8576-1	Linux kernel (NVIDIA Tegra) vulnerabilities
Ubuntu USN	USN-8574-2	Linux kernel vulnerabilities
Ubuntu USN	USN-8595-1	Linux kernel (Oracle) vulnerabilities
Ubuntu USN	USN-8596-1	Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN	USN-8575-2	Linux kernel vulnerabilities
Ubuntu USN	USN-8576-2	Linux kernel (NVIDIA Tegra) vulnerabilities
Ubuntu USN	USN-8597-1	Linux kernel (IBM) vulnerabilities
Ubuntu USN	USN-8575-3	Linux kernel vulnerabilities
Ubuntu USN	USN-8595-2	Linux kernel (AWS) vulnerabilities
Ubuntu USN	USN-8606-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-8607-1	Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN	USN-8608-1	Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN	USN-8609-1	Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN	USN-8610-1	Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN	USN-8574-3	Linux kernel vulnerabilities
Ubuntu USN	USN-8595-3	Linux kernel (AWS) vulnerabilities
Ubuntu USN	USN-8619-1	Linux kernel (HWE) vulnerabilities
Ubuntu USN	USN-8620-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8620-2	Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN	USN-8620-3	Linux kernel (Intel IoTG) vulnerabilities
Ubuntu USN	USN-8620-4	Linux kernel (Intel IoTG) vulnerabilities
Ubuntu USN	USN-8665-1	Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN	USN-8668-1	Linux kernel (GCP) vulnerabilities
Ubuntu USN	USN-8668-2	Linux kernel (Raspberry Pi) vulnerabilities

Metrics

No CVSS v4.0

Attack Vector Local

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction Required

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.143% probability within 30 days)

Exploitation none

Automatable no

Technical Impact total

References

Link	Providers
https://cert-portal.siemens.com/productcert/html/ssa-019113.html
https://cert-portal.siemens.com/productcert/html/ssa-082556.html
https://cert-portal.siemens.com/productcert/html/ssa-457936.html
https://git.kernel.org/stable/c/3822743dc20386d9897e999dbb990befa3a5b3f8
https://git.kernel.org/stable/c/3a926957cc95899ef88529710836edadc03c71a1
https://git.kernel.org/stable/c/5ad6d994255e27a3254079dfb50ca861fc31f2d0
https://git.kernel.org/stable/c/7b58c110b4e1f028eb38eec9ed3555e9be81c8b0
https://git.kernel.org/stable/c/7d5b04290156c3fc316eecc86a4f9d201ab7d44a
https://git.kernel.org/stable/c/ad1f6d608f33f59d21a3d025615d6786a6443998
https://git.kernel.org/stable/c/b77de3fceafbb39f30e4ff5dc986f863d5456417
https://git.kernel.org/stable/c/d787d3ae96648dc14a3b7ca8fde817177e82c1c7
https://lore.kernel.org/linux-cve-announce/2026042246-CVE-2026-31447-ed33@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2026-31447
https://www.cve.org/CVERecord?id=CVE-2026-31447

History

Oct 19, 2026 7:30 PM Weaknesses updated View changes

Type	Values Removed	Values Added
Weaknesses		CWE-20

Oct 16, 2026 4:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}`

Oct 15, 2026 2:30 AM Added references View changes

Type	Values Removed	Values Added
References		https://cert-portal.siemens.com/productcert/html/ssa-457936.html

May 7, 2026 7:30 PM Weaknesses updated. Affected versions updated View changes

Type	Values Removed	Values Added
Weaknesses		NVD-CWE-noinfo
CPEs		cpe:2.3:o:linux:linux_kernel:7.0:rc1:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc2:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc3:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc4:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc5::::::

Apr 27, 2026 2:15 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics	cvssV3_1 `{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}`	cvssV3_1 `{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'}`

Apr 23, 2026 12:15 AM Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Weaknesses		CWE-1288
References		https://lore.kernel.org/linux-cve-announce/2026042246-CVE-2026-31447-ed33@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2026-31447 https://www.cve.org/CVERecord?id=CVE-2026-31447
Metrics	threat_severity `None`	cvssV3_1 `{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}` threat_severity `Moderate`

Apr 22, 2026 2:15 PM Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references View changes

Type	Values Removed	Values Added
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.
Title		ext4: reject mount if bigalloc with s_first_data_block != 0
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/3822743dc20386d9897e999dbb990befa3a5b3f8 https://git.kernel.org/stable/c/3a926957cc95899ef88529710836edadc03c71a1 https://git.kernel.org/stable/c/5ad6d994255e27a3254079dfb50ca861fc31f2d0 https://git.kernel.org/stable/c/7b58c110b4e1f028eb38eec9ed3555e9be81c8b0 https://git.kernel.org/stable/c/7d5b04290156c3fc316eecc86a4f9d201ab7d44a https://git.kernel.org/stable/c/ad1f6d608f33f59d21a3d025615d6786a6443998 https://git.kernel.org/stable/c/b77de3fceafbb39f30e4ff5dc986f863d5456417 https://git.kernel.org/stable/c/d787d3ae96648dc14a3b7ca8fde817177e82c1c7