CriticalCVE-2021-23383

Prototype Pollution (CVE-2021-23383)

Published 04.05.2021Last modified 08.10.2026Sources: CVE.org, OSV

What is affected, what to do

The package handlebars before 4.7.7 are vulnerable to Prototype Pollution when selecting certain compiling options to compile templates coming from an untrusted source.

Update Handlebars to version 4.7.7.

Affected: Handlebars lt *..4.7.7
Fixed in: Handlebars 4.7.7

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

9.8

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v3

5.6

CVSS v3

Severity Medium on the scale from 0 to 10.

Source: CVE.org, OSV

4.5 %

EPSS score

Moderate — model estimates 1-10% exploitation likelihood.

Source: FIRST EPSS, percentile 91.5

Show all metrics

Severity: Critical
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 94.98 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 9.8 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 5.6
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 4.5 %; Moderate — model estimates 1-10% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 91.5; Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 04.05.2021
CISA assessment (SSVC): Exploitation: none known · automatable · Technical impact: total; Source: CISA Vulnrichment, as of 8 October 2026

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

The package handlebars before 4.7.7 are vulnerable to Prototype Pollution when selecting certain compiling options to compile templates coming from an untrusted source.

Source: cvelistv5, NVD (NIST), OSV (Open Source Vulnerabilities)

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
—	handlebars	`< 4.7.7`	`4.7.7`
handlebarsjs	handlebars	`< 4.7.7`	`4.7.7`
netapp	e-series_performance_analyzer	`—`	—

Vendors and products

References & sources

NVD (NIST)vuln/detail/CVE-2021-23383advisory
github.comhandlebars-lang/handlebars.js/commit/f0589701698268578199be2528…web, x_refsource_MISC
github.comhandlebars-lang/handlebars.jspackage
github.comrubysec/ruby-advisory-db/blob/master/gems/handlebars-source/CVE…web
security.netapp.comadvisory/ntap-20210618-0007web
snyk.iovuln/SNYK-JAVA-ORGWEBJARS-1279031web, x_refsource_MISC
snyk.iovuln/SNYK-JAVA-ORGWEBJARSBOWER-1279032web, x_refsource_MISC
snyk.iovuln/SNYK-JAVA-ORGWEBJARSNPM-1279030web, x_refsource_MISC
snyk.iovuln/SNYK-JS-HANDLEBARS-1279029web, x_refsource_MISC
npmjs.compackage/handlebarsweb
security.netapp.comadvisory/ntap-20210618-0007x_refsource_CONFIRM

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

08.10.2026Record modifiedsnyk.io

New references:

and 2 more references

Show 18 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/handlebars-lang/handlebars.js/commit/f0589701698268578199be25285b2ebea1c1e427
Reference	added	—	https://security.netapp.com/advisory/ntap-20210618-0007/
Reference	added	—	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARS-1279031
Reference	added	—	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSBOWER-1279032
Reference	added	—	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-1279030
Reference	added	—	https://snyk.io/vuln/SNYK-JS-HANDLEBARS-1279029
Reference	removed	https://github.com/handlebars-lang/handlebars.js/commit/f0589701698268578199be25285b2ebea1c1e427	—
Reference	removed	https://security.netapp.com/advisory/ntap-20210618-0007/	—
Reference	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARS-1279031	—
Reference	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSBOWER-1279032	—
Reference	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-1279030	—
Reference	removed	https://snyk.io/vuln/SNYK-JS-HANDLEBARS-1279029	—
Reference type	removed	https://github.com/handlebars-lang/handlebars.js/commit/f0589701698268578199be25285b2ebea1c1e427 Types: Patch, Third Party Advisory	—
Reference type	removed	https://security.netapp.com/advisory/ntap-20210618-0007/ Types: Third Party Advisory	—
Reference type	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARS-1279031 Types: Exploit, Patch, Third Party Advisory	—
Reference type	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSBOWER-1279032 Types: Exploit, Patch, Third Party Advisory	—
Reference type	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-1279030 Types: Exploit, Patch, Third Party Advisory	—
Reference type	removed	https://snyk.io/vuln/SNYK-JS-HANDLEBARS-1279029 Types: Exploit, Patch, Third Party Advisory	—

Source identifier: report@snyk.io

08.10.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: none known, automatable: yes

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
SSVC assessment	added	—	{"id":"CVE-2021-23383","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-10-08T21:03:53.835330Z"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

08.10.2026Record modifiedCVE Program

New references:

and 2 more references

Show 18 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/handlebars-lang/handlebars.js/commit/f0589701698268578199be25285b2ebea1c1e427
Reference	added	—	https://security.netapp.com/advisory/ntap-20210618-0007/
Reference	added	—	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARS-1279031
Reference	added	—	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSBOWER-1279032
Reference	added	—	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-1279030
Reference	added	—	https://snyk.io/vuln/SNYK-JS-HANDLEBARS-1279029
Reference	removed	https://github.com/handlebars-lang/handlebars.js/commit/f0589701698268578199be25285b2ebea1c1e427	—
Reference	removed	https://security.netapp.com/advisory/ntap-20210618-0007/	—
Reference	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARS-1279031	—
Reference	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSBOWER-1279032	—
Reference	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-1279030	—
Reference	removed	https://snyk.io/vuln/SNYK-JS-HANDLEBARS-1279029	—
Reference type	removed	https://github.com/handlebars-lang/handlebars.js/commit/f0589701698268578199be25285b2ebea1c1e427 Types: Patch, Third Party Advisory	—
Reference type	removed	https://security.netapp.com/advisory/ntap-20210618-0007/ Types: Third Party Advisory	—
Reference type	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARS-1279031 Types: Exploit, Patch, Third Party Advisory	—
Reference type	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSBOWER-1279032 Types: Exploit, Patch, Third Party Advisory	—
Reference type	removed	https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-1279030 Types: Exploit, Patch, Third Party Advisory	—
Reference type	removed	https://snyk.io/vuln/SNYK-JS-HANDLEBARS-1279029 Types: Exploit, Patch, Third Party Advisory	—

Source identifier: af854a3a-2127-422b-91ae-364da2661108

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<a href="https://intel.neosec.eu/en/cve/CVE-2021-23383"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-23383.svg?lang=en" alt="CVE-2021-23383 – NEOSEC Intel" height="20"></a>