CVE-2025-62494

Code execution via stale string operand type

Published Oct 16, 2025 · Updated Oct 16, 2025

Type confusion in QuickJS 2025-04-26 allows attackers to corrupt memory and execute code through crafted JavaScript string addition. JS_ConcatStringInPlace checks the left operand as a string, calls JS_ToPrimitiveFree on the right operand, then reuses the stale type assumption after a conversion callback changes the left operand type. Exploitation requires a low-privileged execution context that evaluates crafted JavaScript; successful memory corruption executes code in the QuickJS runtime context.

CVSS severity7.1
High
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Type confusion in QuickJS 2025-04-26 allows attackers to corrupt memory and execute code through crafted JavaScript string addition. JS_ConcatStringInPlace checks the left operand as a string, calls JS_ToPrimitiveFree on the right operand, then reuses the stale type assumption after a conversion callback changes the left operand type. Exploitation requires a low-privileged execution context that evaluates crafted JavaScript; successful memory corruption executes code in the QuickJS runtime context.

The record

CVE
CVE-2025-62494
Published
Oct 16, 2025
Updated
Oct 16, 2025
Vendor
Fabrice Bellard
Product
QuickJS
Classifications
CWE-704, CAPEC-175, T1203
Attack vector
adjacent
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 16, 2025Record 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=2025-04-26 <2025-09-13

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesauthenticated

What is affected?

Fabrice Bellard · QuickJSversion=2025-04-26 <2025-09-13

Published CVSS scores

7.1Google Inc.CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L
8.8NIST National Vulnerability DatabaseCVSS:3.1/AV:A/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)
Vectoradjacent
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-704Incorrect Type Conversion or Cast
CAPEC-175Code Inclusion
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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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