CVE-2021-23383Public exploitNetwork attack vector

Arbitrary JavaScript execution via unescaped compat property names

Published May 4, 2021 · Updated Sep 16, 2024

Prototype pollution in Handlebars.js before 4.7.7 allows attackers to inject code through templates compiled with the compat option. The JavaScriptCompiler depthedLookup path places a template property name inside generated JavaScript without string-safe encoding, so quotes in that name escape the lookup expression. Exploitation requires an untrusted template and the non-default compat option; injected JavaScript then runs when the generated template executes.

CVSS severity9.8
Critical
EPSS probability4.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Prototype pollution in Handlebars.js before 4.7.7 allows attackers to inject code through templates compiled with the compat option. The JavaScriptCompiler depthedLookup path places a template property name inside generated JavaScript without string-safe encoding, so quotes in that name escape the lookup expression. Exploitation requires an untrusted template and the non-default compat option; injected JavaScript then runs when the generated template executes.

The record

CVE
CVE-2021-23383
Published
May 4, 2021
Updated
Sep 16, 2024
Vendor
Handlebars
Product
Handlebars.js
Classifications
CWE-1321, CAPEC-1, CAPEC-180
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 4, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <4.7.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Handlebars · Handlebars.jsversion=unspecified <4.7.7

Published CVSS scores

9.8GitLab Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
5.6CVE ProgramCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L/E:P/RL:O/RC:C

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
CAPEC-1Accessing Functionality Not Properly Constrained by ACLs
CAPEC-180Exploiting Incorrectly Configured Access Control Security Levels

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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