CVE-2019-9803
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.56%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.0
- 7.4 HIGHCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- EPSS
- 0.56% probability · 46th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-346
- Affected
- mozilla/firefox
- Source
- security@mozilla.org
EPSS 0.6% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
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
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.