CVE-2017-7820 — The "instanceof" operator can bypass the Xray wrapper mechanism

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. Thi

01What is this vulnerability?

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.

02Affected products

Vendor	Product	Versions
Mozilla	Firefox	unspecified

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2018-06-11T21:00:00.000Z
• Last modified: 2024-08-05T16:12:28.355Z

09References

• www.securitytracker.com — http://www.securitytracker.com/id/1039465
• bugzilla.mozilla.org — https://bugzilla.mozilla.org/show_bug.cgi?id=1378207
• www.mozilla.org — https://www.mozilla.org/security/advisories/mfsa2017-21/
• www.securityfocus.com — http://www.securityfocus.com/bid/101057