CVE-2021-43453Public exploitNetwork attack vector

Engine crash via unterminated for-let parsing

Published Apr 7, 2022 · Updated Aug 4, 2024

Out-of-bounds read in the JerryScript parser in JerryScript 2.4.0 and earlier allows attackers to crash the engine with malformed JavaScript. In parser_parse_for_statement_start, an unterminated for-let statement reaches a scanner-state comparison before the LEXER_KEYW_LET token is handled, causing a one-byte read beyond heap bounds. Execution of attacker-controlled JavaScript is required; the demonstrated consequence is a segmentation-fault crash, with no demonstrated code execution or data disclosure.

CVSS severity9.8
Critical
EPSS probability1.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in the JerryScript parser in JerryScript 2.4.0 and earlier allows attackers to crash the engine with malformed JavaScript. In parser_parse_for_statement_start, an unterminated for-let statement reaches a scanner-state comparison before the LEXER_KEYW_LET token is handled, causing a one-byte read beyond heap bounds. Execution of attacker-controlled JavaScript is required; the demonstrated consequence is a segmentation-fault crash, with no demonstrated code execution or data disclosure.

The record

CVE
CVE-2021-43453
Published
Apr 7, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-125, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 7, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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-125Out-of-bounds Read
T1499Endpoint Denial of Service

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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