CVE-2026-100803 Mozilla Firefox - Same-Origin Policy Bypass

Mozilla Firefox WebExtensions component contains a same-origin policy bypass vulnerability, letting attackers bypass same-origin restrictions, exploit requires crafted web content.

CVSS base score 8.1 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.19% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Same-Origin Policy Bypass
Impact
Information Disclosure
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Published
29 September 2026
Updated
15 October 2026
Weakness
CWE-346

Vendor fix

Update to Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, Firefox ESR 140.17 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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