CVE-2026-16381Network attack vector

Unauthenticated cross-origin data access

Published Jul 21, 2026 · Updated Jul 21, 2026

Same-origin policy bypass in Firefox and Thunderbird before 153 allows remote attackers to access cross-origin data through DNS handling. Mozilla identifies the Networking: DNS component but has not published the flawed DNS operation or the input that triggers the origin-validation failure. The issue is remotely reachable without authentication or user interaction; ESR releases before 140.13 are also affected, with no reported service interruption.

CVSS severity9.1
Critical
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Same-origin policy bypass in Firefox and Thunderbird before 153 allows remote attackers to access cross-origin data through DNS handling. Mozilla identifies the Networking: DNS component but has not published the flawed DNS operation or the input that triggers the origin-validation failure. The issue is remotely reachable without authentication or user interaction; ESR releases before 140.13 are also affected, with no reported service interruption.

The record

CVE
CVE-2026-16381
Published
Jul 21, 2026
Updated
Jul 21, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-346
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.

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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-346Origin Validation Error

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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