How severe is CVE-2021-40865?

CVE-2021-40865 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-40865?

CVE-2021-40865 affects the following packages: org.apache.storm:storm (Maven), org.apache.storm:storm (Maven), org.apache.storm:storm (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-40865?

Update org.apache.storm:storm to 2.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-40865 is resolved across your whole dependency graph.

How do I detect CVE-2021-40865 in my Maven dependencies?

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

How do I mitigate CVE-2021-40865 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Is CVE-2021-40865 actively exploited in the wild?

Yes. There are 2 known exploit references for CVE-2021-40865, 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-2021-40865?

CVE-2021-40865 has an EPSS (Exploit Prediction Scoring System) score of 64.2%, placing it in the 99th 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. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2021-40865?

CVE-2021-40865 is classified as Deserialization of Untrusted Data (CWE-502). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2021-40865 published, and has it been updated?

CVE-2021-40865 was published on October 25, 2021 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

CRITICAL severity

CVE-2021-40865 — storm

CRITICAL

CVE-2021-40865 is a critical-severity (CVSS 9.8) Deserialization of Untrusted Data vulnerability in org.apache.storm:storm. 2 public exploit references exist, so weaponization risk is real. A fix is available for org.apache.storm:storm — see the affected versions and patch details below.

Deserialization of Untrusted Data leading to Remote Code Execution in Apache Storm

Also known asGHSA-w729-7633-2fw5

Published

Oct 25, 2021

Updated

Jul 9, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

2 known

Exploitation data as of Oct 12, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

64.2%probability of exploitation in next 30 days

High Risk0.00%

Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-40865 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

3 pkgs affected

☕org.apache.storm:storm☕org.apache.storm:storm☕org.apache.storm:storm

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

Description

An Unsafe Deserialization vulnerability exists in the worker services of the Apache Storm supervisor server allowing pre-auth Remote Code Execution (RCE). Apache Storm 2.2.x users should upgrade to version 2.2.1 or 2.3.0. Apache Storm 2.1.x users should upgrade to version 2.1.1. Apache Storm 1.x users should upgrade to version 1.2.4

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.storm:storm`	≥ 2.2.0&&< 2.2.1	2.2.1`org.apache.storm:storm:2.2.1`
☕Maven	`org.apache.storm:storm`	≥ 1.0.0&&< 1.2.4	1.2.4`org.apache.storm:storm:1.2.4`
☕Maven	`org.apache.storm:storm`	≥ 2.1.0&&< 2.1.1	2.1.1`org.apache.storm:storm:2.1.1`

Affected Products

1 product · 3 configurations

Application

stormapache

≥ 2.2.0 && < 2.2.1

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.

An Unsafe Deserialization vulnerability exists in the worker services of…

github.comGithubNov 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.storm:storm, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.storm:storm to 2.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-40865 is resolved across your whole dependency graph.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-40865 in your dependencies?

Find it across Maven, including transitive dependencies.

Scan my dependencies How O3 SCA works

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-502Deserialization of Untrusted Data

Weaponization

No known public exploit tooling found.

Timeline

Disclosed

Oct 25, 2021

First exploit

Nov 26, 2021

Last updated

Jul 9, 2026

Identifiers

CVE-2021-40865

GHSA-w729-7633-2fw5

References

Advisorylists.apache.org Advisoryseclists.org Advisorynvd.nist.gov

Related vulnerabilities

Also affects storm

This CVE is critical severity; 2 of 3 other CVEs affecting storm are rated as high or higher (top: critical).

CVE-2014-0115CVE-2015-3188CVE-2021-38294

Same weakness: CWE-502

This CVE is critical severity; 3 of 5 other CVEs with CWE-502 are rated as high or higher (top: critical).

CVE-2025-66455CVE-2025-59953CVE-2026-49400CVE-2026-50646CVE-2026-78683Browse all CWE-502

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 9, 2026

CVE-2021-40865 — storm

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-2021-40865 in your dependencies?