CVE-2021-29325Public exploit

Runtime crash via oversized repeated string copy

Published Nov 19, 2021 · Updated Aug 3, 2024

Heap buffer overflow in Moddable SDK 10.5.0 allows context-dependent attackers to crash the XS runtime by executing crafted JavaScript. fx_String_prototype_repeat calls memcpy for 1,048,578 bytes at the end of a 16,777,248-byte heap region, overrunning its allocation. The published proof of concept must be executed by xst and produces an AddressSanitizer abort; code execution is not demonstrated.

CVSS severity7.8
High
EPSS probability0.76%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer overflow in Moddable SDK 10.5.0 allows context-dependent attackers to crash the XS runtime by executing crafted JavaScript. fx_String_prototype_repeat calls memcpy for 1,048,578 bytes at the end of a 16,777,248-byte heap region, overrunning its allocation. The published proof of concept must be executed by xst and produces an AddressSanitizer abort; code execution is not demonstrated.

The record

CVE
CVE-2021-29325
Published
Nov 19, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1204.002
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Nov 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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 privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8NIST National Vulnerability DatabaseCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:P/I:P/A:P

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
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1204.002Malicious File

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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