CVE-2026-16390Network attack vector

Enterprise policy enforcement bypass

Published Jul 21, 2026 · Updated Jul 21, 2026

Mitigation bypass in Mozilla Firefox and Thunderbird allows remote attackers to defeat enterprise policy enforcement. Mozilla has not disclosed which Enterprise Policies function mishandles attacker-controlled input or which policy controls can be bypassed. Managed deployments are exposed in Firefox and Thunderbird before 153 and Firefox ESR and Thunderbird ESR before 140.13.

CVSS severity9.1
Critical
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Mitigation bypass in Mozilla Firefox and Thunderbird allows remote attackers to defeat enterprise policy enforcement. Mozilla has not disclosed which Enterprise Policies function mishandles attacker-controlled input or which policy controls can be bypassed. Managed deployments are exposed in Firefox and Thunderbird before 153 and Firefox ESR and Thunderbird ESR before 140.13.

The record

CVE
CVE-2026-16390
Published
Jul 21, 2026
Updated
Jul 21, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-693
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 21, 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

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

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

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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