CVE-2026-98636 - Vulnerability Details

- squashfs: Add dictionary size range check to prevent shift-out-of-bounds

Description

In the Linux kernel, the following vulnerability has been resolved:

squashfs: Add dictionary size range check to prevent shift-out-of-bounds

When an abnormal SquashFS image (COMP_OPTS flag is 1 but dictionary size
is 0) is mounted, and performs shift operations using dictionarysize, the
shift exponent is -1, causing a shift-out-of-bounds.

Detail as below:
squashfs_comp_opts(msblk, buffer, length)
squashfs_xz_comp_opts()
if (comp_opts)
n = ffs(opts->dict_size) - 1;<----opts->dict_size=0, n=-1
if (opts->dict_size != (1 << n) && opts->dict_size !=
(1 << n) + (1 << (n + 1))) <----shift-out-of-bounds

Fix it by adding a dictionary size range check before the shift operation.

Published: 2026-10-18

Score: 4.4 Medium

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

A malformed SquashFS image that sets the COMP_OPTS flag to 1 with a dictionary size of zero causes the kernel’s squashfs module to perform a left shift with a negative exponent. This shift-out-of-bounds condition corrupts kernel memory. The vulnerability does not explicitly provide a mechanism for arbitrary code execution, but memory corruption could lead to privilege escalation or a system crash if an attacker mounts such an image.

Affected Systems

All Linux kernel releases that include the squashfs filesystem compiled with the COMP_OPTS option enabled and accept images with a dictionary size of zero are affected. Versions that do not apply the patch adding a dictionary size range check remain vulnerable.

Risk and Exploitability

The CVSS score of 4.4 indicates a moderate impact; the EPSS score is less than 1 % and it is not listed in CISA’s KEV catalog. Exploitation requires local capability to mount a crafted SquashFS image, making it a local privilege escalation or denial‑of‑service vulnerability rather than a remote attack vector.

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
`ff750311d30acc9564ef577050794953eee59f01`	affected	< b02948a23455f8190a53887b2d2c13ae1d360cea
`ff750311d30acc9564ef577050794953eee59f01`	affected	< 9d9c5c218ea356a1d88765214ad2919605280ab1
`ff750311d30acc9564ef577050794953eee59f01`	affected	< 7a1c293e7aa17f1afaee0684e0e931fe23a5a6b1
`ff750311d30acc9564ef577050794953eee59f01`	affected	< c68e0068a236f9a7dfc19720bdf11e5d80a85089
`ff750311d30acc9564ef577050794953eee59f01`	affected	< 88c673a0bd233df44ca0020da82f4fd3876de27a
`ff750311d30acc9564ef577050794953eee59f01`	affected	< 0cb85377daaefb4ce5ce72975f2deb27ee0e0cad
`ff750311d30acc9564ef577050794953eee59f01`	affected	< e1ca4e3a380ef3e8f46ce006f1146392e3f32c98
`ff750311d30acc9564ef577050794953eee59f01`	affected	< 1f7745fb3580152ca902ef181b605f33cabfb1d0

Linux

affected

Version	Status	Constraints
`2.6.39`	affected	—
`0`	unaffected	< 2.6.39
`5.10.271`	unaffected	≤ 5.10.*
`5.15.222`	unaffected	≤ 5.15.*
`6.1.189`	unaffected	≤ 6.1.*
`6.6.158`	unaffected	≤ 6.6.*
`6.12.112`	unaffected	≤ 6.12.*
`6.18.55`	unaffected	≤ 6.18.*
`7.2.9`	unaffected	≤ 7.2.*
`7.3`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[ff750311d30acc9564ef577050794953eee59f01,b02948a23455f8190a53887b2d2c13ae1d360cea)`	affected	code_commit	—
`[ff750311d30acc9564ef577050794953eee59f01,9d9c5c218ea356a1d88765214ad2919605280ab1)`	affected	code_commit	—
`[ff750311d30acc9564ef577050794953eee59f01,7a1c293e7aa17f1afaee0684e0e931fe23a5a6b1)`	affected	code_commit	—
`[ff750311d30acc9564ef577050794953eee59f01,c68e0068a236f9a7dfc19720bdf11e5d80a85089)`	affected	code_commit	—
`[ff750311d30acc9564ef577050794953eee59f01,88c673a0bd233df44ca0020da82f4fd3876de27a)`	affected	code_commit	—
`[ff750311d30acc9564ef577050794953eee59f01,0cb85377daaefb4ce5ce72975f2deb27ee0e0cad)`	affected	code_commit	—
`[ff750311d30acc9564ef577050794953eee59f01,e1ca4e3a380ef3e8f46ce006f1146392e3f32c98)`	affected	code_commit	—
`[ff750311d30acc9564ef577050794953eee59f01,1f7745fb3580152ca902ef181b605f33cabfb1d0)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`2.6.39`	affected	semver	—
`[0,2.6.39)`	unaffected	semver	—
`[5.10.271,5.11.0)`	unaffected	semver	—
`[5.15.222,5.16.0)`	unaffected	semver	—
`[6.1.189,6.2.0)`	unaffected	semver	—
`[6.6.158,6.7.0)`	unaffected	semver	—
`[6.12.112,6.13.0)`	unaffected	semver	—
`[6.18.55,6.19.0)`	unaffected	semver	—
`[7.2.9,7.3.0)`	unaffected	semver	—
`[7.3-rc5,*]`	unaffected	generic	—

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Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Apply the kernel patch that implements the dictionary size range check before any shift operations in squasfs_comp_opts().
If a patch is not yet available, disable the COMP_OPTS option for squashfs filesystems or ensure that any image mounted has a non‑zero dictionary size.
Validate SquashFS image metadata before mounting to detect a dictionary size of zero and reject or repair such images.

Generated by OpenCVE AI on October 23, 2026 at 06:35 UTC.

Tracking

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Advisories

Source	ID	Title
Debian DLA	DLA-4850-1	linux-6.12 security update
Ubuntu USN	USN-8961-1	Linux kernel vulnerabilities

No CVSS v4.0

Attack Vector Local

Attack Complexity Low

Privileges Required High

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00177.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98636.mbox
https://git.kernel.org/stable/c/0cb85377daaefb4ce5ce72975f2deb27ee0e0cad
https://git.kernel.org/stable/c/1f7745fb3580152ca902ef181b605f33cabfb1d0
https://git.kernel.org/stable/c/7a1c293e7aa17f1afaee0684e0e931fe23a5a6b1
https://git.kernel.org/stable/c/88c673a0bd233df44ca0020da82f4fd3876de27a
https://git.kernel.org/stable/c/9d9c5c218ea356a1d88765214ad2919605280ab1
https://git.kernel.org/stable/c/b02948a23455f8190a53887b2d2c13ae1d360cea
https://git.kernel.org/stable/c/c68e0068a236f9a7dfc19720bdf11e5d80a85089
https://git.kernel.org/stable/c/e1ca4e3a380ef3e8f46ce006f1146392e3f32c98
https://nvd.nist.gov/vuln/detail/CVE-2026-98636
https://www.cve.org/CVERecord?id=CVE-2026-98636

History

Fri, 23 Oct 2026 00:45:00 +0000

Type	Values Removed	Values Added
Weaknesses	CWE-190 CWE-788

Thu, 22 Oct 2026 12:30:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-1335
References		https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98636.mbox https://nvd.nist.gov/vuln/detail/CVE-2026-98636 https://www.cve.org/CVERecord?id=CVE-2026-98636
Metrics	threat_severity `None`	cvssV3_1 `{'score': 4.4, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H'}` threat_severity `Moderate`

Sun, 18 Oct 2026 18:30:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-190 CWE-788

Sun, 18 Oct 2026 15:30:00 +0000

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: squashfs: Add dictionary size range check to prevent shift-out-of-bounds When an abnormal SquashFS image (COMP_OPTS flag is 1 but dictionary size is 0) is mounted, and performs shift operations using dictionarysize, the shift exponent is -1, causing a shift-out-of-bounds. Detail as below: squashfs_comp_opts(msblk, buffer, length) squashfs_xz_comp_opts() if (comp_opts) n = ffs(opts->dict_size) - 1;<----opts->dict_size=0, n=-1 if (opts->dict_size != (1 << n) && opts->dict_size != (1 << n) + (1 << (n + 1))) <----shift-out-of-bounds Fix it by adding a dictionary size range check before the shift operation.
Title		squashfs: Add dictionary size range check to prevent shift-out-of-bounds
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/0cb85377daaefb4ce5ce72975f2deb27ee0e0cad https://git.kernel.org/stable/c/1f7745fb3580152ca902ef181b605f33cabfb1d0 https://git.kernel.org/stable/c/7a1c293e7aa17f1afaee0684e0e931fe23a5a6b1 https://git.kernel.org/stable/c/88c673a0bd233df44ca0020da82f4fd3876de27a https://git.kernel.org/stable/c/9d9c5c218ea356a1d88765214ad2919605280ab1 https://git.kernel.org/stable/c/b02948a23455f8190a53887b2d2c13ae1d360cea https://git.kernel.org/stable/c/c68e0068a236f9a7dfc19720bdf11e5d80a85089 https://git.kernel.org/stable/c/e1ca4e3a380ef3e8f46ce006f1146392e3f32c98

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-10-18T15:20:07.184Z

Updated: 2026-10-19T09:23:06.005Z

Reserved: 2026-09-25T10:25:14.361Z

Link: CVE-2026-98636

Vulnrichment

No data.

NVD

Status : Received

Published: 2026-10-18T16:17:16.700

Modified: 2026-10-19T10:19:27.837

Link: CVE-2026-98636

Redhat

Severity : Moderate

Publid Date: 2026-10-18T00:00:00Z

Links: CVE-2026-98636 - Bugzilla

OpenCVE Enrichment

Updated: 2026-10-23T06:45:07Z

Weaknesses

CWE-1335
Incorrect Bitwise Shift of Integer

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Local

Attack Complexity Low

Privileges Required High

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

Subscriptions

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