CVE-2019-9803

Name: CVE-2019-9803
Creator: NVD / NIST
Published: 2019-04-26T17:29:03.257+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

UnknownEPSS 0.56%

Last modified Jun 17, 2026

CVE-2019-9803 is a vulnerability of currently unknown severity. 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. EPSS estimates a 0.56% chance of exploitation in the next 30 days.

Description

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.

Metrics

EPSS Probability

0.56%

42.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-346

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 66.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1437009Issue Tracking, Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1515863Issue Tracking, Permissions Required, Vendor Advisory
https://w3c.github.io/webappsec-upgrade-insecure-requests/Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2019-07/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1437009Issue Tracking, Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1515863Issue Tracking, Permissions Required, Vendor Advisory
https://w3c.github.io/webappsec-upgrade-insecure-requests/Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2019-07/Vendor Advisory

Timeline

Published: Apr 26, 2019
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2019-9803?

How severe is CVE-2019-9803?

Severity scoring for CVE-2019-9803 is pending analysis. The EPSS model estimates a 0.56% probability of exploitation in the next 30 days.

How do I fix CVE-2019-9803?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2019-9803?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST