CVE-2023-6861Public exploitNetwork attack vector

Process crash via invalid headless window cast

Published Dec 19, 2023 · Updated Feb 13, 2025

Heap buffer overflow in Mozilla Firefox before 121, Firefox ESR before 115.6, and Thunderbird before 115.6 allows attackers to crash the process. Headless mode leaves the nsIWidget without a backing nsWindow, but nsWindow::PickerOpen uses static_cast and reads four bytes from unrelated heap memory. Triggering requires Windows headless mode, a file-picker request, and custom preferences; ordinary interactive sessions are unaffected.

CVSS severity8.8
High
EPSS probability1.41%
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 Mozilla Firefox before 121, Firefox ESR before 115.6, and Thunderbird before 115.6 allows attackers to crash the process. Headless mode leaves the nsIWidget without a backing nsWindow, but nsWindow::PickerOpen uses static_cast and reads four bytes from unrelated heap memory. Triggering requires Windows headless mode, a file-picker request, and custom preferences; ordinary interactive sessions are unaffected.

The record

CVE
CVE-2023-6861
Published
Dec 19, 2023
Updated
Feb 13, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 19, 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 <121

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <121
Mozilla · Thunderbirdversion=unspecified <115.6
Mozilla · Firefox ESRversion=unspecified <115.6

Published CVSS scores

8.8NIST National Vulnerability DatabaseCVSS: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 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 exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

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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