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CVE-2017-7821

31
FAUCET Score

CVE-2017-7821 is a critical vulnerability affecting Firefox versions prior to 56, where WebExtensions can download and open non-executable files without explicit user interaction. This could lead to the exploitation of vulnerabilities in the programs handling those document types. With a CVSS score of 9.8 (CRITICAL), it presents a high-impact threat with network-based, low-complexity attacks potentially leading to complete compromise of confidentiality, integrity, and availability. While there is no known active exploitation or public exploit code, the vulnerability has garnered significant community discussion, indicating awareness and potential interest.

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

9.8CRITICAL

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.0

Exploit Intelligence

EPSS Score
1.98%
Probability of exploitation in next 30 days
EPSS Percentile
78.4%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0198 is in the 67th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 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