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CVE-2021-23984

MEDIUM
6.5
CVSS Score
Published: March 31, 2021 at 01:41 PM UTC
Updated: June 17, 2026 at 03:39 AM UTC
3 products affected across 1 vendorFirefoxThunderbirdFirefox ESR

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Severity
MEDIUM6.5
Exploit prediction
EPSS 1%

Description

A malicious extension could have opened a popup window lacking an address bar. The title of the popup lacking an address bar should not be fully controllable, but in this situation was. This could have been used to spoof a website and attempt to trick the user into providing credentials. This vulnerability affects Firefox ESR < 78.9, Firefox < 87, and Thunderbird < 78.9.

Affected

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

Firefox· Mozilla
95%
v < 87
Affected range stops below 87, so it looks safe — our inference, not a vendor statement
Affected range stops below 87.0, so it looks safe — our inference, not a vendor statement
Firefox ESR· Mozilla
95%
v < 78.9
Affected range stops below 78.9, so it looks safe — our inference, not a vendor statement
Thunderbird· Mozilla
95%
v < 78.9
Affected range stops below 78.9, so it looks safe — our inference, not a vendor statement

References (4)

x_refsource_MISCIssue TrackingVendor Advisory
Source: [email protected]
https://bugzilla.mozilla.org/show_bug.cgi?id=1693664
x_refsource_MISCVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-10/
x_refsource_MISCVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-11/
x_refsource_MISCVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-12/

CVSS

6.5MEDIUM[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
NONE
Integrity
HIGH
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-290

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