How severe is CVE-2021-36440?

CVE-2021-36440 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-36440?

CVE-2021-36440 affects the following packages: showdoc/showdoc (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-36440?

Update showdoc/showdoc to 2.9.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-36440 is resolved across your whole dependency graph.

How do I detect CVE-2021-36440 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for showdoc/showdoc, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-36440 if there is no patch (or I can't update yet)?

Treat uploaded files as untrusted until proven otherwise: validate the actual content type rather than the supplied extension, store uploads outside the web root on a volume mounted without execute permission, and rename them to server-generated identifiers so an attacker cannot choose the path a request will later resolve.

Is CVE-2021-36440 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-36440, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-36440?

CVE-2021-36440 has an EPSS (Exploit Prediction Scoring System) score of 4.8%, placing it in the 92th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-36440?

CVE-2021-36440 is classified as Unrestricted File Upload (CWE-434). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-36440 published, and has it been updated?

CVE-2021-36440 was published on September 8, 2021 and was last updated on August 7, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

Not in CISA KEV

CRITICAL severity

CVE-2021-36440 — showdoc

CRITICALFix: star7th/showdoc@49b992d

CVE-2021-36440 is a critical-severity (CVSS 9.8) Unrestricted File Upload vulnerability in showdoc/showdoc. 1 public exploit reference exists, so weaponization risk is real. A fix is available for showdoc/showdoc — see the affected versions and patch details below.

Unrestricted File Upload in ShowDoc v2.9.5

Also known asGHSA-c442-3278-rhrg

Published

Sep 8, 2021

Updated

Aug 7, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

4.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs92th percentile — riskier than 92% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-36440 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐘showdoc/showdoc

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

Unrestricted File Upload in ShowDoc v2.9.5 allows remote attackers to execute arbitrary code via the 'file_url' parameter in the component AdminUpdateController.class.php'.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`showdoc/showdoc`	all versions	2.9.6`composer require showdoc/showdoc:^2.9.6`

Affected Products

1 product · 1 configurations

Application

showdocshowdoc

1 version

2.9.5

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Unrestricted File Upload in ShowDoc v2.9.5 allows remote attackers to ex…

github.comNVDSep 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for showdoc/showdoc, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update showdoc/showdoc to 2.9.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-36440 is resolved across your whole dependency graph.
Workarounds
Treat uploaded files as untrusted until proven otherwise: validate the actual content type rather than the supplied extension, store uploads outside the web root on a volume mounted without execute permission, and rename them to server-generated identifiers so an attacker cannot choose the path a request will later resolve.

Frequently Asked Questions

Unrestricted File Upload in ShowDoc v2.9.5 allows remote attackers to execute arbitrary code via the 'file_url' parameter in the component AdminUpdateController.class.php'.

O3 Security · Impact-Aware SCA

Is CVE-2021-36440 in your dependencies?

Find it across Packagist, including transitive dependencies.

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CVSS Score

9.8/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Raw vector

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

CWE Classification

CWE-434Unrestricted File Upload

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

showdoc

4.3/10

Maintained10/10

Code-Review1/10

Branch-Protection0/10

Assessed Oct 5, 2026

Timeline

Disclosed

Sep 8, 2021

First exploit

Sep 15, 2021

7 days after disclosure — rapid exploitation

Last updated

Aug 7, 2026

Identifiers

CVE-2021-36440

GHSA-c442-3278-rhrg

References

Advisorynvd.nist.gov Reportgithub.com Webgithub.com Packagegithub.com

Related vulnerabilities

This CVE is critical severity; 1 of 8 other CVEs affecting showdoc/showdoc is rated as high or higher (top: critical).

CVE-2026-6982CVE-2025-0520CVE-2018-16342CVE-2018-19621CVE-2018-19609CVE-2018-19620CVE-2022-1034CVE-2022-0967

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedAug 7, 2026

CVE-2021-36440 — showdoc

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-36440 in your dependencies?