CVE-2021-46522Public exploit

Heap over-read via crafted substring search

Published Jan 27, 2022 · Updated Aug 4, 2024

Heap-buffer over-read in Cesanta MJS 2.20.0 allows local users to read past a heap allocation by executing crafted JavaScript. During String.indexOf evaluation, mg_strstr performs a 19-byte read starting at the end of a 107-byte allocation. The attacker must cause interpreter execution of the crafted script; public evidence demonstrates a sanitizer-detected over-read but no data disclosure or code execution.

CVSS severity7.8
High
EPSS probability0.73%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-buffer over-read in Cesanta MJS 2.20.0 allows local users to read past a heap allocation by executing crafted JavaScript. During String.indexOf evaluation, mg_strstr performs a 19-byte read starting at the end of a 107-byte allocation. The attacker must cause interpreter execution of the crafted script; public evidence demonstrates a sanitizer-detected over-read but no data disclosure or code execution.

The record

CVE
CVE-2021-46522
Published
Jan 27, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 27, 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 vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write

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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