CVE-2021-23969
If that’s not possible, user agents need to strip the URL down to an origin to avoid unintentional leakage." Under certain types of redirects, Firefox incorrectly set the source file to be the destination of the redirects.
Does this matter?
Lower severity and a low EPSS score (1.21%). Track it; it rarely justifies an emergency change on its own.
Description
As specified in the W3C Content Security Policy draft, when creating a violation report, "User agents need to ensure that the source file is the URL requested by the page, pre-redirects. If that’s not possible, user agents need to strip the URL down to an origin to avoid unintentional leakage." Under certain types of redirects, Firefox incorrectly set the source file to be the destination of the redirects. This was fixed to be the redirect destination's origin. This vulnerability affects Firefox < 86, Thunderbird < 78.8, and Firefox ESR < 78.8.
- CVSS 3.1
- 4.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
- EPSS
- 1.21% probability · 68th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Affected
- mozilla/firefox · mozilla/firefox esr · mozilla/thunderbird · debian/debian linux
- Source
- security@mozilla.org
EPSS 1.2% 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=1542194Issue Tracking, Permissions Required, Vendor Advisory
- https://lists.debian.org/debian-lts-announce/2021/03/msg00000.htmlMailing List, Third Party Advisory
- https://security.gentoo.org/glsa/202104-09Third Party Advisory
- https://security.gentoo.org/glsa/202104-10Third Party Advisory
- https://www.debian.org/security/2021/dsa-4866Third Party Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-07/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-08/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-09/Release Notes, Vendor Advisory
- https://bugzilla.mozilla.org/show_bug.cgi?id=1542194Issue Tracking, Permissions Required, Vendor Advisory
- https://lists.debian.org/debian-lts-announce/2021/03/msg00000.htmlMailing List, Third Party Advisory
- https://security.gentoo.org/glsa/202104-09Third Party Advisory
- https://security.gentoo.org/glsa/202104-10Third Party Advisory
- https://www.debian.org/security/2021/dsa-4866Third Party Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-07/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-08/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-09/Release Notes, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.