CVE-2026-84127Network attack vector

Private-session data disclosure via misclassified extension tabs

Published Sep 1, 2026 · Updated Sep 1, 2026

Information disclosure in Firefox for Android before 155 allows attackers to recover private-session data left by extension-created tabs. The tabs.create() path fails to propagate the privateMode flag, so Fenix labels a tab private while GeckoView loads its content in regular browsing state. An installed extension must create a tab while private browsing is active; cookies, cache, and other site data can remain in regular storage for later extraction from the device.

CVSS severity4.3
Medium
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Firefox for Android before 155 allows attackers to recover private-session data left by extension-created tabs. The tabs.create() path fails to propagate the privateMode flag, so Fenix labels a tab private while GeckoView loads its content in regular browsing state. An installed extension must create a tab while private browsing is active; cookies, cache, and other site data can remain in regular storage for later extraction from the device.

The record

CVE
CVE-2026-84127
Published
Sep 1, 2026
Updated
Sep 1, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-200
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

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

4.3CISA ADP VulnrichmentCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/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 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-200Exposure of Sensitive Information to an Unauthorized Actor

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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