CVE-2020-26958
Firefox did not block execution of scripts with incorrect MIME types when the response was intercepted and cached through a ServiceWorker.
Does this matter?
Lower severity and a low EPSS score (1.36%). Track it; it rarely justifies an emergency change on its own.
Description
Firefox did not block execution of scripts with incorrect MIME types when the response was intercepted and cached through a ServiceWorker. This could lead to a cross-site script inclusion vulnerability, or a Content Security Policy bypass. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.
- CVSS 3.1
- 6.1 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- EPSS
- 1.36% probability · 72th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-79
- Affected
- mozilla/firefox · mozilla/firefox esr · mozilla/thunderbird
- Source
- security@mozilla.org
EPSS 1.4% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1669355Issue Tracking, Permissions Required, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2020-50/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2020-51/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2020-52/Vendor Advisory
- https://bugzilla.mozilla.org/show_bug.cgi?id=1669355Issue Tracking, Permissions Required, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2020-50/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2020-51/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2020-52/Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.