How severe is CVE-2021-41495?

CVE-2021-41495 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-41495?

CVE-2021-41495 affects the following packages: numpy (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2021-41495?

Update numpy to 1.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41495 is resolved across your whole dependency graph.

How do I detect CVE-2021-41495 in my PyPI dependencies?

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

How do I mitigate CVE-2021-41495 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2021-41495 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-41495, 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-2021-41495?

CVE-2021-41495 has an EPSS (Exploit Prediction Scoring System) score of 1.2%, placing it in the 69th 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-2021-41495?

CVE-2021-41495 is classified as NULL Pointer Dereference (CWE-476). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-41495 published, and has it been updated?

CVE-2021-41495 was published on December 17, 2021 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

MEDIUM severity

CVE-2021-41495 — numpy

MEDIUM

CVE-2021-41495 is a medium-severity (CVSS 5.3) NULL Pointer Dereference vulnerability in numpy. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for numpy — see the affected versions and patch details below.

NumPy NULL Pointer Dereference

Also known asGHSA-5545-2q6w-2gh6PYSEC-2021-856

Published

Dec 17, 2021

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

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

EPSS Exploitation Probability

via FIRST.org ↗

1.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs69th percentile — riskier than 69% of all scored CVEsHighest risk

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐍numpy

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

Description

Null Pointer Dereference vulnerability exists in numpy.sort in NumPy &lt and 1.19 in the PyArray_DescrNew function due to missing return-value validation, which allows attackers to conduct DoS attacks by repetitively creating sort arrays. NOTE: While correct that validation is missing, an error can only occur due to an exhaustion of memory. If the user can exhaust memory, they are already privileged. Further, it should be practically impossible to construct an attack which can target the memory exhaustion to occur at exactly this place

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`numpy`	all versions	1.19`pip install --upgrade 'numpy==1.19'`

Affected Products

1 product · 1 configurations

Application

numpynumpy

≤ 1.19.0

range

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.

Null Pointer Dereference vulnerability exists in numpy.sort in NumPy &lt…

github.comNVDDec 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for numpy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update numpy to 1.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41495 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Product	Fixed in	Advisory
Red Hat OpenStack Platform 16.1	`numpy-1:1.17.0-11.el8ost`	RHSA-2022:8861
Red Hat OpenStack Platform 16.2	`numpy-1:1.17.0-11.el8ost`	RHSA-2022:8852

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-41495 in your dependencies?

Find it across PyPI, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

5.3/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

High

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Raw vector

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

CWE Classification

CWE-476NULL Pointer Dereference

Weaponization

No Nuclei template or Metasploit module yet. 1 public proof-of-concept reference is listed on this page.

OpenSSF Scorecard

Package health score

numpy

7.9/10

Dependency-Update-Tool10/10

Maintained10/10

Code-Review9/10

Vulnerabilities10/10

Branch-Protection3/10

Assessed Nov 7, 2026

Timeline

Disclosed

Dec 17, 2021

First exploit

Dec 22, 2021

5 days after disclosure — rapid exploitation

Last updated

Oct 20, 2026

Identifiers

CVE-2021-41495

GHSA-5545-2q6w-2gh6

PYSEC-2021-856

References

Advisoryoracle.com · cpujul2022 Advisorynvd.nist.gov · CVE 2021 41495 Advisorygithub.com · GHSA 5545 2q6w 2gh6 Reportgithub.com Webgithub.com · PYSEC 2021 856.yaml Packagegithub.com · numpy

Related vulnerabilities

Also affects numpy

This CVE is medium severity; 7 of 7 other CVEs affecting numpy are rated as high or higher (top: critical).

CVE-2019-6446CVE-2014-1859CVE-2014-1858CVE-2017-12852CVE-2021-41496CVE-2021-33430CVE-2021-34141

Same weakness: CWE-476

This CVE is medium severity, in line with the other 1 CVE with CWE-476.

CVE-2026-125334Browse all CWE-476

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 20, 2026

CVE-2021-41495 — numpy

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

Fixing This On Your OS

Frequently Asked Questions

Is CVE-2021-41495 in your dependencies?