CVE-2026-3846Public exploitNetwork attack vector

Cross-origin CSS access via origin-clean flag reset

Published Mar 10, 2026 · Updated Mar 10, 2026

Same-origin policy bypass in Mozilla Firefox before 148.0.2 allows remote attackers to access cross-origin CSS through a crafted webpage. StyleSheetInfo's copy constructor omits mOriginClean, so cloning a shared cross-origin stylesheet resets the flag to true and passes CSSOM checks. A user must load the attacker's content; the bypass exposes CSS rules and redirect destination URLs and permits CSSOM rule changes.

CVSS severity6.5
Medium
EPSS probability0.11%
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 Mozilla Firefox before 148.0.2 allows remote attackers to access cross-origin CSS through a crafted webpage. StyleSheetInfo's copy constructor omits mOriginClean, so cloning a shared cross-origin stylesheet resets the flag to true and passes CSSOM checks. A user must load the attacker's content; the bypass exposes CSS rules and redirect destination URLs and permits CSSOM rule changes.

The record

CVE
CVE-2026-3846
Published
Mar 10, 2026
Updated
Mar 10, 2026
Vendor
Mozilla
Product
Firefox
Classifications
CWE-346, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 10, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <148.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <148.0.2

Published CVSS scores

6.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/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 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 exploitPublished

Weakness, pattern, technique

CWE-346Origin Validation Error
T1189Drive-by Compromise

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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