CVE-2026-8401Network attack vector

Unauthenticated sandbox escape

Published May 12, 2026 · Updated May 12, 2026

Sandbox escape in Mozilla Firefox and Thunderbird allows remote attackers to break Profile Backup process isolation via unspecified vectors. Mozilla has not disclosed the faulty operation or attacker-controlled input in Profile Backup that defeats the sandbox in Firefox before 150.0.3, Firefox ESR before 115.36 and 140.11, and Thunderbird before 140.11. Published assessments agree that no privileges are required but disagree on user interaction, and capabilities after escape remain undisclosed.

CVSS severity9.8
Critical
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Sandbox escape in Mozilla Firefox and Thunderbird allows remote attackers to break Profile Backup process isolation via unspecified vectors. Mozilla has not disclosed the faulty operation or attacker-controlled input in Profile Backup that defeats the sandbox in Firefox before 150.0.3, Firefox ESR before 115.36 and 140.11, and Thunderbird before 140.11. Published assessments agree that no privileges are required but disagree on user interaction, and capabilities after escape remain undisclosed.

The record

CVE
CVE-2026-8401
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-693, T1068
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5Red Hat SADPCVSS:3.1/AV:N/AC:H/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-693Protection Mechanism Failure
T1068Exploitation for Privilege Escalation

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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