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CVE-2019-9803

19
FAUCET Score

CVE-2019-9803 describes a vulnerability in Firefox versions prior to 66 where the browser fails to correctly upgrade insecure HTTP requests to HTTPS, despite a Content Security Policy (CSP) enforcing Upgrade-Insecure-Requests (UIR). This flaw allows for potential man-in-the-middle (MitM) attacks on linked resources, as Firefox incorrectly navigates to the HTTP URL. The vulnerability carries a CVSS score of 7.4 (HIGH) due to its network-based attack vector and high impact on confidentiality and integrity, though it requires high attack complexity. Currently, there is no known active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 66.0CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
< 66CPE match
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

7.4HIGH

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
2.2
Impact Score
5.2
CvssVersion
3.0

Exploit Intelligence

EPSS Score
0.56%
Probability of exploitation in next 30 days
EPSS Percentile
43.2%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0056 is in the 16th percentile among its peer group of 8,920 CVEs.

Social Chatter

No social media mentions found for this CVE.

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 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
Issue TrackingVendor Advisory
bugzilla.mozilla.org / show_bug.cgi
Issue TrackingPermissions RequiredVendor Advisory
w3c.github.io / webappsec-upgrade-insecure-requests
Third Party Advisory
mozilla.org / security/advisories/mfsa2019-07
Vendor Advisory