CVE-2026-2778Network attack vector

Sandbox escape via DOM boundary miscalculation

Published Feb 24, 2026 · Updated Feb 24, 2026

Sandbox escape in Mozilla Firefox, Firefox ESR, and Thunderbird allows remote attackers to leave the content sandbox during web-content processing. Mozilla identifies incorrect boundary conditions in DOM Core and HTML, but the access-restricted bug leaves the exact boundary check and malformed input undisclosed. A crafted DOM or HTML workload must reach the affected component; successful exploitation crosses the content sandbox boundary, with resulting host actions not publicly detailed.

CVSS severity10.0
Critical
EPSS probability0.48%
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, Firefox ESR, and Thunderbird allows remote attackers to leave the content sandbox during web-content processing. Mozilla identifies incorrect boundary conditions in DOM Core and HTML, but the access-restricted bug leaves the exact boundary check and malformed input undisclosed. A crafted DOM or HTML workload must reach the affected component; successful exploitation crosses the content sandbox boundary, with resulting host actions not publicly detailed.

The record

CVE
CVE-2026-2778
Published
Feb 24, 2026
Updated
Feb 24, 2026
Vendor
Mozilla
Product
Firefox
Classifications
CWE-119, T1068
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 24, 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

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <148
Mozilla · Thunderbirdversion=unspecified <140.8; version=unspecified <148
Mozilla · Firefox ESRversion=unspecified <115.33; version=unspecified <140.8

Published CVSS scores

10.0CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
7.5redhat-SADPCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
10.0NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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 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-119Improper Restriction of Operations within the Bounds of a Memory Buffer
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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