CVE-2019-9803

Severity: high (CVSS 7.4 v3.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2019-04-26 · updated 2026-06-17
Weakness: CWE-346

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.

Affected products

Mozilla Firefox: before 66.0 — fixed in 66.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 66.0. Check the vendor advisory for mitigations.

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
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/

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