CVE-2026-100803
published 2026-09-29CVE-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…
PriorityP341high8.1CVSS 3.1
AVNACLPRNUIRSUCHIHAN
EPSS
0.19%
7.8th percentile
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.
Affected
11 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| mozilla | firefox | < Firefox 157 | Firefox 157 |
| mozilla | firefox | — | — |
| mozilla | firefox_esr | < Firefox ESR 140.17 | Firefox ESR 140.17 |
| mozilla | firefox_esr | < Firefox ESR 153.4 | Firefox ESR 153.4 |
| mozilla | firefox_esr | < Firefox ESR 115.42 | Firefox ESR 115.42 |
| mozilla | thunderbird | < Thunderbird 157 | Thunderbird 157 |
| mozilla | thunderbird | < Thunderbird 153.4 | Thunderbird 153.4 |
| mozilla | thunderbird | < Thunderbird 140.17 | Thunderbird 140.17 |
| mozilla | thunderbird | — | — |
| rhel10 | firefox-flatpak | — | — |
| rhel10 | thunderbird-flatpak | — | — |
CVSS provenance
nvdv3.18.1HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
vendor_redhat8.1HIGH
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Red Hat
firefox: thunderbird: Same-origin policy bypass in the WebExtensions component
vendor_redhat·2026-09-29·CVSS 8.1
CVE-2026-100803 [HIGH] CWE-346 firefox: thunderbird: Same-origin policy bypass in the WebExtensions component
firefox: thunderbird: Same-origin policy bypass in the WebExtensions component
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.
A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue:
Same-origin policy bypass in the WebExtensions component
Statement: Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.
Mitigation: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applic
Mozilla
Mozilla Foundation Security Advisory 2026-99: CVE-2026-100803
vendor_mozilla
CVE-2026-100803 Mozilla Foundation Security Advisory 2026-99: CVE-2026-100803
Mozilla Foundation Security Advisory 2026-99
CVE: CVE-2026-100803
Product: Firefox ESR
Impact: moderate
Fixed in: Firefox ESR 140.17
Mozilla
Mozilla Foundation Security Advisory 2026-101: CVE-2026-100803
vendor_mozilla
CVE-2026-100803 Mozilla Foundation Security Advisory 2026-101: CVE-2026-100803
Mozilla Foundation Security Advisory 2026-101
CVE: CVE-2026-100803
Product: Thunderbird
Impact: low
Fixed in: Thunderbird 157
Mozilla
Mozilla Foundation Security Advisory 2026-100: CVE-2026-100803
vendor_mozilla
CVE-2026-100803 Mozilla Foundation Security Advisory 2026-100: CVE-2026-100803
Mozilla Foundation Security Advisory 2026-100
CVE: CVE-2026-100803
Product: Firefox ESR
Impact: low
Fixed in: Firefox ESR 153.4
Mozilla
Mozilla Foundation Security Advisory 2026-103: CVE-2026-100803
vendor_mozilla
CVE-2026-100803 Mozilla Foundation Security Advisory 2026-103: CVE-2026-100803
Mozilla Foundation Security Advisory 2026-103
CVE: CVE-2026-100803
Product: Thunderbird
Impact: low
Fixed in: Thunderbird 153.4
Mozilla
Mozilla Foundation Security Advisory 2026-97: CVE-2026-100803
vendor_mozilla
CVE-2026-100803 Mozilla Foundation Security Advisory 2026-97: CVE-2026-100803
Mozilla Foundation Security Advisory 2026-97
CVE: CVE-2026-100803
Product: Firefox
Impact: low
Fixed in: Firefox 157
Mozilla
Mozilla Foundation Security Advisory 2026-102: CVE-2026-100803
vendor_mozilla
CVE-2026-100803 Mozilla Foundation Security Advisory 2026-102: CVE-2026-100803
Mozilla Foundation Security Advisory 2026-102
CVE: CVE-2026-100803
Product: Thunderbird
Impact: moderate
Fixed in: Thunderbird 140.17
Mozilla
Mozilla Foundation Security Advisory 2026-98: CVE-2026-100803
vendor_mozilla
CVE-2026-100803 Mozilla Foundation Security Advisory 2026-98: CVE-2026-100803
Mozilla Foundation Security Advisory 2026-98
CVE: CVE-2026-100803
Product: Firefox ESR
Impact: moderate
Fixed in: Firefox ESR 115.42
GHSA
Same-origin policy bypass in the WebExtensions component.
ghsa_unreviewed·2026-09-29
CVE-2026-100803 Same-origin policy bypass in the WebExtensions component.
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.
No detection rules found.
No public exploits indexed.
https://bugzilla.mozilla.org/show_bug.cgi?id=2057988https://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/https://www.mozilla.org/security/advisories/mfsa2026-97/https://www.mozilla.org/security/advisories/mfsa2026-98/https://www.mozilla.org/security/advisories/mfsa2026-99/
2026-09-29
Published