CVE-2026-100803

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

CVSS 3.1

8.1CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

EPSS

0.2% chance of exploitation in the next 30 days; higher than 5% of CVEs (scores of 2026-10-25)

CWE

CWE-346

Published

2026-09-29

Modified

2026-10-19

Record from

the NVD, synced 2026-10-19

Affected

• mozilla:firefox
• mozilla:thunderbird

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2057988
• https://www.mozilla.org/security/advisories/mfsa2026-100/
• https://www.mozilla.org/security/advisories/mfsa2026-101/
• https://www.mozilla.org/security/advisories/mfsa2026-102/
• https://www.mozilla.org/security/advisories/mfsa2026-103/

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