CVE-2026-100803: Same-origin policy bypass in the WebExtensions component

Published Sep 29, 2026
·
Updated

Same-origin policy bypass in the WebExtensions component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

Affected Software

4 affected componentsFixes available
Mozilla Firefox ESR<115.42
115.42
Mozilla Firefox ESR<140.17
140.17
Mozilla Firefox<157
157
Mozilla Firefox ESR<153.4
153.4

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 115.42
  2. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 140.17
  3. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 157
  4. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 153.4
  5. Upgrade

    Upgrade Firefox ESR to a version that resolves this vulnerability.

    Fixed in 153.4
  6. Upgrade

    Upgrade Firefox to a version that resolves this vulnerability.

    Fixed in 157
  7. Upgrade

    Upgrade Firefox ESR to a version that resolves this vulnerability.

    Fixed in 115.42
  8. Upgrade

    Upgrade Firefox ESR to a version that resolves this vulnerability.

    Fixed in 140.17

Event History

Sep 29, 2026
CVE Published
via Mozilla·12:00 AM
Data Sourced
via Mozilla·12:00 AM
DescriptionSeverityAffected Software
Updated
via Mozilla·12:00 AM
Affected Software
CVE Published
via MITRE·12:36 PM
Data Sourced
via MITRE·12:36 PM
Description
Data Sourced
via NVD·01:17 PM
Description

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

1

Which Firefox releases contain the fix?

The issue was fixed in Firefox 157, Firefox ESR 153.4, Firefox ESR 115.42, and Firefox ESR 140.17.

2

What security boundary can this vulnerability bypass?

It can bypass the same-origin policy in the WebExtensions component.

Company

Resources

Contact

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