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CVE-2017-7820

20
FAUCET Score

CVE-2017-7820 describes a vulnerability in Firefox versions prior to 56 where the "instanceof" operator can bypass the Xray wrapper, allowing web content to manipulate its result and potentially trick the browser or extensions. This medium-severity vulnerability has a CVSS score of 5.3, indicating a network-based attack with low complexity, requiring no user interaction, and potentially leading to a loss of integrity. There is no evidence of active exploitation, and no public exploit code is available in Metasploit, Nuclei, or ExploitDB. Community discussion is minimal, with only one mention on Reddit.

Impacted Technologies

VendorProductVersion(s)CPE
<= 55.0.3CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
< 56CPE match
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

5.3MEDIUM

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.0

Exploit Intelligence

EPSS Score
1.19%
Probability of exploitation in next 30 days
EPSS Percentile
64.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0119 is in the 43rd percentile among its peer group of 23,723 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Vendor Patches (1)

mozillavendor investigatingvia nvd_reference
View patch

References

bugzilla.mozilla.org / show_bug.cgi
ExploitIssue Tracking
mozilla.org / security/advisories/mfsa2017-21
Vendor Advisory
securityfocus.com / bid/101057
Third Party AdvisoryVDB Entry
securitytracker.com / id/1039465
Third Party AdvisoryVDB Entry