CVE-2019-9803

7.4 highEPSS 0.6%

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.

Severity

CVSS 3.0

7.4 high

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

EPSS: 0.6% chance of exploitation in the next 30 days; higher than 46% of CVEs (scores of 2026-10-31)
CWE: CWE-346
Published: 2019-04-26
Modified: 2026-06-17
Record from: the NVD, synced 2026-10-19

Affected

mozilla:firefox

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1437009
https://bugzilla.mozilla.org/show_bug.cgi?id=1515863
https://w3c.github.io/webappsec-upgrade-insecure-requests/
https://www.mozilla.org/security/advisories/mfsa2019-07/
https://bugzilla.mozilla.org/show_bug.cgi?id=1437009

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