CVE-2023-4049Network attack vector

Browser interruption via reference-counting double free

Published Aug 1, 2023 · Updated Feb 13, 2025

Use-after-free in Mozilla Firefox before 116 and Firefox ESR before 102.14 or 115.1 allows remote attackers to interrupt the browser. The nsHtml5OwningUTF16Buffer Release implementation performs multiple atomic loads, allowing two threads to decrement a count of two, both observe zero, and double-free the object. Triggering requires concurrent object destruction; Mozilla notes that web content can create and destroy these objects despite their lack of direct exposure.

CVSS severity5.9
Medium
EPSS probability0.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Mozilla Firefox before 116 and Firefox ESR before 102.14 or 115.1 allows remote attackers to interrupt the browser. The nsHtml5OwningUTF16Buffer Release implementation performs multiple atomic loads, allowing two threads to decrement a count of two, both observe zero, and double-free the object. Triggering requires concurrent object destruction; Mozilla notes that web content can create and destroy these objects despite their lack of direct exposure.

The record

CVE
CVE-2023-4049
Published
Aug 1, 2023
Updated
Feb 13, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-362, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 1, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 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=unspecified <116

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <116
Mozilla · Firefox ESRversion=unspecified <102.14; version=unspecified <115.1

Published CVSS scores

5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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