How severe is CVE-2021-41496?

CVE-2021-41496 has a CVSS score of 5.5/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-41496?

CVE-2021-41496 affects the following packages: numpy (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2021-41496?

Update numpy to 1.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41496 is resolved across your whole dependency graph.

How do I detect CVE-2021-41496 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-2021-41496 if there is no patch (or I can't update yet)?

Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Is CVE-2021-41496 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-41496, 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-2021-41496?

CVE-2021-41496 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 32th 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-2021-41496?

CVE-2021-41496 is classified as CWE-120 (CWE-120). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-41496 published, and has it been updated?

CVE-2021-41496 was published on December 17, 2021 and was last updated on July 25, 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-2021-41496 — numpy

MEDIUM

CVE-2021-41496 is a medium-severity (CVSS 5.5) CWE-120 vulnerability in numpy. 1 public exploit reference exists, so weaponization risk is real. A fix is available for numpy — see the affected versions and patch details below.

Buffer Copy without Checking Size of Input in NumPy

Also known asGHSA-f7c7-j99h-c22fPYSEC-2021-857

Published

Dec 17, 2021

Updated

Jul 25, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk+0.03%

Lower risk than most CVEs32th percentile — riskier than 32% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-41496 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 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

🐍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

Buffer overflow in the array_from_pyobj function of fortranobject.c in NumPy < 1.19, which allows attackers to conduct a Denial of Service attacks by carefully constructing an array with negative values. NOTE: The vendor does not agree this is a vulnerability; the negative dimensions can only be created by an already privileged user (or internally)

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.

Buffer overflow in the array_from_pyobj function of fortranobject.c in N…

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-2021-41496 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

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-1:1.17.0-8.el8ost`	RHSA-2022:0987
Red Hat OpenStack Platform 16.2	`numpy-1:1.17.0-8.el8ost`	RHSA-2022:1000

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-41496 in your dependencies?

Find it across PyPI, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

5.5/10CVSS v3 base

Vector breakdown

Attack Vector

Local

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Raw vector

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

CWE Classification

CWE-120CWE-120

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

numpy

7.9/10

Code-Review10/10

Maintained10/10

Dependency-Update-Tool10/10

Branch-Protection3/10

Vulnerabilities9/10

Assessed Oct 11, 2026

Timeline

Disclosed

Dec 17, 2021

First exploit

Dec 27, 2021

Last updated

Jul 25, 2026

Identifiers

CVE-2021-41496

GHSA-f7c7-j99h-c22f

PYSEC-2021-857

References

Advisoryoracle.com Advisorynvd.nist.gov Fixgithub.com Packagegithub.com

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-2021-41495CVE-2021-33430CVE-2021-34141

Same weakness: CWE-120

This CVE is medium severity; 1 of 1 other CVE with CWE-120 is rated as high or higher (top: critical).

CVE-2026-55209Browse all CWE-120

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 25, 2026

CVE-2021-41496 — 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-2021-41496 in your dependencies?