vulntracker.iovulntracker.io
© 2026 vulntracker.io

CVE-2021-23969

MEDIUM
4.3
CVSS Score
Published: February 26, 2021 at 01:57 AM UTC
Updated: June 17, 2026 at 03:39 AM UTC
4 products affected across 2 vendorsDebian LinuxFirefoxThunderbird

Using Firefox by Mozilla?

Get instant alerts when new vulnerabilities affect Firefox - before attackers find them.

Real-time alertsTrack your software stackFree plan available
Start FreeSign In
Severity
MEDIUM4.3
Exploit prediction
EPSS 1%

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Debian Linux· Debiandrupal
95%
10.09.0
Firefox· Mozilla
95%
v < 86
Affected range stops below 86, so it looks safe — our inference, not a vendor statement
Affected range stops below 86.0, so it looks safe — our inference, not a vendor statement
Firefox ESR· Mozilla
95%
v < 78.8
Affected range stops below 78.8, so it looks safe — our inference, not a vendor statement
Thunderbird· Mozilla
95%
v < 78.8
Affected range stops below 78.8, so it looks safe — our inference, not a vendor statement

References (8)

x_refsource_MISCIssue TrackingPermissions RequiredVendor Advisory
Source: [email protected]
https://bugzilla.mozilla.org/show_bug.cgi?id=1542194
Mailing Listx_refsource_MLISTThird Party Advisory
Source: [email protected]
https://lists.debian.org/debian-lts-announce/2021/03/msg00000.html
Vendor Advisoryx_refsource_GENTOOThird Party Advisory
Source: [email protected]
https://security.gentoo.org/glsa/202104-09
Vendor Advisoryx_refsource_GENTOOThird Party Advisory
Source: [email protected]
https://security.gentoo.org/glsa/202104-10
Vendor Advisoryx_refsource_DEBIANThird Party Advisory
Source: [email protected]
https://www.debian.org/security/2021/dsa-4866
x_refsource_MISCRelease NotesVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-07/
x_refsource_MISCRelease NotesVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-08/
x_refsource_MISCRelease NotesVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-09/

CVSS

4.3MEDIUM[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
LOW
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
NVD-CWE-noinfo

Get alerted

Stop reading CVE feeds looking for your own stack

Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.

Create accountSign in
Free plan, no card