CVE-2023-6205Network attack vector

Application crash via freed MessagePort access

Published Nov 21, 2023 · Updated Feb 13, 2025

MessagePort use-after-free in affected Firefox and Thunderbird releases allows remote attackers to crash the application via web content. MessagePort::Entangled can access a MessagePort after its storage has been freed, leaving the content process to dereference invalid heap memory. A user must load attacker-controlled active content; Thunderbird message reading disables scripting, so ordinary email display does not expose this path.

CVSS severity6.5
Medium
EPSS probability0.87%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

MessagePort use-after-free in affected Firefox and Thunderbird releases allows remote attackers to crash the application via web content. MessagePort::Entangled can access a MessagePort after its storage has been freed, leaving the content process to dereference invalid heap memory. A user must load attacker-controlled active content; Thunderbird message reading disables scripting, so ordinary email display does not expose this path.

The record

CVE
CVE-2023-6205
Published
Nov 21, 2023
Updated
Feb 13, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-416, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 21, 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 <120

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <120
Mozilla · Thunderbirdversion=unspecified <115.5
Mozilla · Firefox ESRversion=unspecified <115.5.0

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/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.

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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-416Use After Free
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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