CVE-2017-7820
The "instanceof" operator can bypass the Xray wrapper mechanism.
Does this matter?
Lower severity and a low EPSS score (1.16%). Track it; it rarely justifies an emergency change on its own.
Description
The "instanceof" operator can bypass the Xray wrapper mechanism. When called on web content from the browser itself or an extension the web content can provide its own result for that operator, possibly tricking the browser or extension into mishandling the element. This vulnerability affects Firefox < 56.
- CVSS 3.0
- 5.3 MEDIUMCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- EPSS
- 1.16% probability · 67th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Affected
- mozilla/firefox
- Source
- security@mozilla.org
EPSS 1.2% since 27 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
- http://www.securityfocus.com/bid/101057Third Party Advisory, VDB Entry
- http://www.securitytracker.com/id/1039465Third Party Advisory, VDB Entry
- https://bugzilla.mozilla.org/show_bug.cgi?id=1378207Exploit, Issue Tracking
- https://www.mozilla.org/security/advisories/mfsa2017-21/Vendor Advisory
- http://www.securityfocus.com/bid/101057Third Party Advisory, VDB Entry
- http://www.securitytracker.com/id/1039465Third Party Advisory, VDB Entry
- https://bugzilla.mozilla.org/show_bug.cgi?id=1378207Exploit, Issue Tracking
- https://www.mozilla.org/security/advisories/mfsa2017-21/Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.