CVE-2026-8879Network attack vector

Browsing interruption via fail-closed content overlay

Published Jun 3, 2026 · Updated Jun 3, 2026

Denial of service in Securly Chrome Extension 3.0.7 and earlier allows remote attackers to hide all page content on managed Chromebooks. The undeclared content13.min.js script is registered at runtime for every URL, hides page content behind a full-page overlay, pauses videos, and restores content only after a service-worker filtering check. When the extension is active on a school-managed Chrome OS device and Securly servers are unreachable, the overlay remains indefinitely and interrupts browsing.

CVSS severity7.5
High
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Securly Chrome Extension 3.0.7 and earlier allows remote attackers to hide all page content on managed Chromebooks. The undeclared content13.min.js script is registered at runtime for every URL, hides page content behind a full-page overlay, pauses videos, and restores content only after a service-worker filtering check. When the extension is active on a school-managed Chrome OS device and Securly servers are unreachable, the overlay remains indefinitely and interrupts browsing.

The record

CVE
CVE-2026-8879
Published
Jun 3, 2026
Updated
Jun 3, 2026
Vendor
Securly
Product
Securly Chrome Extension
Classifications
CWE-829, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 3, 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=0 <=3.0.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Securly · Securly Chrome Extensionversion=0 <=3.0.7

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 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-829Inclusion of Functionality from Untrusted Control Sphere
T1499Endpoint Denial of Service

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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