CVE-2026-100803Same-origin policy bypass in the WebExtensions component
Updated under an hour ago ()
Does this affect you?
It affects Mozilla Firefox and 1 other product. Add what you run to find out whether that includes you.
EPSS puts the chance of exploitation in the next 30 days at 0.19%, higher than 8% of scored CVEs.
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Free account, 1 product
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
- 8.1 HIGH (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
- Weakness (CWE)
- CWE-346
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- 0.19% (percentile 8)
- Assigned by
- mozilla
- NVD analysis
- Undergoing Analysis
- Record last updated
- Oct 1, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Mozilla Firefox mozilla:firefox (from the name) | 115.42 builds before 115.* not affected; 140.17 builds before 140.* not affected; 153.4 builds before 153.* not affected; from 157 not affected | CNA record |
Mozilla Thunderbird mozilla:thunderbird (from the name) | 140.17 builds before 140.* not affected; 153.4 builds before 153.* not affected; from 157 not affected | CNA record |
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/
- https://www.mozilla.org/security/advisories/mfsa2026-97/
- https://www.mozilla.org/security/advisories/mfsa2026-98/
- https://www.mozilla.org/security/advisories/mfsa2026-99/
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.