The Upgrade-Insecure-Requests (UIR) specification states that if UIR is enabled through Content Security Policy (CSP), navigation to a same…

published 2019-04-26 7 y ago modified 2026-06-17 4 mo ago also EUVD-2019-19165

cvss: 7.4; version 3.0, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.6%; EPSS 0.6% chance of exploitation in 30 days, percentile 46%
public exploits: 0; none known

The Upgrade-Insecure-Requests (UIR) specification states that if UIR is enabled through Content Security Policy (CSP), navigation to a same-origin URL must be upgraded to HTTPS. Firefox will incorrectly navigate to an HTTP URL rather than perform the security upgrade requested by the CSP in some circumstances, allowing for potential man-in-the-middle attacks on the linked resources. This vulnerability affects Firefox < 66.

Patch / fix

fixed in 1 distros 3

Mozilla Firefox 66

ubuntu opensuse arch linux

firefox Ubuntu 14.04 LTS 66.0.1+build1-0ubuntu0.14.04.1
firefox Ubuntu 16.04 LTS 66.0+build3-0ubuntu0.16.04.2
firefox Ubuntu 18.04 LTS 66.0+build3-0ubuntu0.18.04.1

ubuntu advisories UBUNTU-CVE-2019-9803

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

firefox-esr openSUSE Tumbleweed 128.5.1-1.1
MozillaFirefox openSUSE Tumbleweed 92.0-1.2

opensuse advisories openSUSE-SU-2024:14572-1 openSUSE-SU-2024:10600-1

firefox Arch Linux 66.0-1

arch linux advisories AVG-925

Exploit prediction

0.56% chance of exploitation in the next 30 days, higher than 46% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.0	7.4	CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD	2.0	5.8	AV:N/AC:M/Au:N/C:P/I:P/A:N

Affected products

Mozilla Firefox

Classification

Weakness

CWE-346 Origin Validation Error

References

mozilla.org /security/advisories/mfsa2019-07/
vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=1515863
issue-tracking, permissions-required, vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=1437009
issue-tracking, vendor-advisory
w3c.github.io /webappsec-upgrade-insecure-requests/
third-party-advisory

Sources

CVE List CVE-2019-9803
NVD CVE-2019-9803

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary