CVE-2023-6207Network attack vector

Memory corruption via ReadableByteStream buffer use-after-free

Published Nov 21, 2023 · Updated Feb 13, 2025

Use-after-free in Mozilla Firefox before 120, Firefox ESR before 115.5.0, and Thunderbird before 115.5 allows attackers to corrupt memory. Ownership mismanagement causes ReadableByteStreamQueueEntry::Buffer to be accessed after its backing memory has been freed. A user must load attacker-controlled browser-like content; Thunderbird disables scripting while reading email, limiting that path.

CVSS severity8.8
High
EPSS probability0.79%
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 120, Firefox ESR before 115.5.0, and Thunderbird before 115.5 allows attackers to corrupt memory. Ownership mismanagement causes ReadableByteStreamQueueEntry::Buffer to be accessed after its backing memory has been freed. A user must load attacker-controlled browser-like content; Thunderbird disables scripting while reading email, limiting that path.

The record

CVE
CVE-2023-6207
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

8.8NIST NVDCVSS:3.1/AV:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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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