NVD / CVE Program· CNA mitre

CVE-2021-40153: squashfs_opendir in unsquash-1.c in Squashfs-Tools 4.5 stores the filename in the directory entry; this is then used by unsquashfs to create

Noroxi assessment

Priority: Monitor (action score 33/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 2.5% (FIRST EPSS); higher than 84.7% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
Fixed version: squashfs-tools (AlmaLinux:8) 4.3-21.el8; squashfs-tools (AlmaLinux:9) 4.4-10.git1.el9; squashfs-tools (Alpine:v3.11) 4.5-r0.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to squashfs-tools (AlmaLinux:8) 4.3-21.el8; squashfs-tools (AlmaLinux:9) 4.4-10.git1.el9; squashfs-tools (Alpine:v3.11) 4.5-r0 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

squashfs_opendir in unsquash-1.c in Squashfs-Tools 4.5 stores the filename in the directory entry; this is then used by unsquashfs to create the new file during the unsquash. The filename is not validated for traversal outside of the destination directory, and thus allows writing to locations outside of the destination.

HighCVSS 8.1 · v3.1—No exploit Fix available

Published: Aug 27, 2021
Updated: Jun 17, 2026
EPSS: 2.5% · 84th percentile
CWE: CWE-22

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 32 / 40 · 8.1 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 1 / 30 · 2.5%

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Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
squashfs-tools project	squashfs-tools	cpe:2.3:a:squashfs-tools_project:squashfs-tools
fedoraproject	fedora	cpe:2.3:o:fedoraproject:fedora
debian	debian linux	cpe:2.3:o:debian:debian_linux
redhat	enterprise linux	cpe:2.3:o:redhat:enterprise_linux

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

debian debian linux10.0
debian debian linux9.0
fedoraproject fedora33
fedoraproject fedora34
redhat enterprise linux7.0
redhat enterprise linux8.0
squashfs-tools project squashfs-tools4.5

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
AlmaLinux:8	squashfs-tools	before 4.3-21.el8	4.3-21.el8
AlmaLinux:9	squashfs-tools	before 4.4-10.git1.el9	4.4-10.git1.el9
Alpine:v3.11	squashfs-tools	before 4.5-r0	4.5-r0
Debian:10	squashfs-tools	before 1:4.3-12+deb10u1	1:4.3-12+deb10u1
Debian:11	squashfs-tools	before 1:4.4-2+deb11u1	1:4.4-2+deb11u1
Debian:12	squashfs-tools	before 1:4.5-2	1:4.5-2
Debian:9	squashfs-tools	before 1:4.3-3+deb9u2	1:4.3-3+deb9u2
openSUSE:Leap Micro 5.3	squashfs	before 4.6.1-150300.3.3.1	4.6.1-150300.3.3.1
openSUSE:Tumbleweed	squashfs	before 4.6.1-2.1	4.6.1-2.1
Red Hat:enterprise_linux:8::baseos	squashfs-tools	before 0:4.3-21.el8	0:4.3-21.el8
Red Hat:enterprise_linux:8::baseos	squashfs-tools-debuginfo	before 0:4.3-21.el8	0:4.3-21.el8
Red Hat:enterprise_linux:8::baseos	squashfs-tools-debugsource	before 0:4.3-21.el8	0:4.3-21.el8
Red Hat:enterprise_linux:9::baseos	squashfs-tools	before 0:4.4-10.git1.el9	0:4.4-10.git1.el9
Red Hat:enterprise_linux:9::baseos	squashfs-tools-debuginfo	before 0:4.4-10.git1.el9	0:4.4-10.git1.el9
Red Hat:enterprise_linux:9::baseos	squashfs-tools-debugsource	before 0:4.4-10.git1.el9	0:4.4-10.git1.el9
Rocky Linux:8	squashfs-tools	before 0:4.3-21.el8	0:4.3-21.el8
Rocky Linux:9	squashfs-tools	before 0:4.4-10.git1.el9	0:4.4-10.git1.el9
SUSE:Linux Enterprise Micro 5.3	squashfs	before 4.6.1-150300.3.3.1	4.6.1-150300.3.3.1
SUSE:Linux Enterprise Server 12 SP5	squashfs	before 4.6.1-8.3.2	4.6.1-8.3.2

Same product

squashfs-tools project: all records

Other highest-scoring records for the same primary product.

CVE-2021-41072squashfs_opendir in unsquash-2.c in Squashfs-Tools 4.5 allows Directory Traversal, a different vulnerability than CVE-2021-40153.
33Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
almalinux:squashfs-tools	4.4-10.git1.el9 · AlmaLinux:9	Package registry (OSV)
alpine:squashfs-tools	4.5-r0 · Alpine:v3.11	Package registry (OSV)
debian:squashfs-tools	1:4.5-2 · Debian:12	Package registry (OSV)
opensuse:squashfs	4.6.1-150300.3.3.1 · openSUSE:Leap Micro 5.3	Package registry (OSV)
red hat:squashfs-tools	0:4.4-10.git1.el9 · Red Hat:enterprise_linux:9::baseos	Package registry (OSV)
red hat:squashfs-tools-debuginfo	0:4.4-10.git1.el9 · Red Hat:enterprise_linux:9::baseos	Package registry (OSV)
red hat:squashfs-tools-debugsource	0:4.4-10.git1.el9 · Red Hat:enterprise_linux:9::baseos	Package registry (OSV)
rocky linux:squashfs-tools	0:4.4-10.git1.el9 · Rocky Linux:9	Package registry (OSV)
suse:squashfs	4.6.1-150300.3.3.1 · SUSE:Linux Enterprise Micro 5.3	Package registry (OSV)
suse:squashfs	4.6.1-8.3.2 · SUSE:Linux Enterprise Server 12 SP5	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

plougher/squashfs-toolscommit 79b5a55

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-21-0745 · Sep 16, 2021(Ubuntu Güvenlik Bildirimi Yayınladı)

All national notices →

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
A user must open a link or visit a page.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: Required
Scope: Unchanged
Confidentiality impact: None
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-22 · Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H

nvd-primary

Root cause

A user-supplied file name is joined with the allowed directory, but the result is never checked to confirm it is still inside that directory.

The bug in code

The whole CWE-22 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const file = path.join(ROOT, req.query.name);
2res.sendFile(file);

Fixed

1const file = path.resolve(ROOT, req.query.name);
2if (!file.startsWith(ROOT + path.sep)) {
3  return res.sendStatus(400);
4}
5res.sendFile(file);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 10:47 PM UTC

For records you follow, these changes also arrive as notifications. →

References

bugs.launchpad.net/ubuntu/+source/squashfs-tools/+bug/1941790

Show all references (6 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records