#VU50879 Improperly implemented security check for standard in Mozilla Firefox and Firefox ESR - CVE-2021-23969

Vulnerability identifier: #VU50879

Vulnerability risk: Medium

CVSSv4.0: 1.2 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-23969

CWE-ID: CWE-358

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Mozilla Firefox
Client/Desktop applications / Web browsers
Firefox ESR
Client/Desktop applications / Web browsers

Vendor: Mozilla

Description

The vulnerability allows a remote attacker to bypass implemented security restrictions.

The vulnerability exists due to incorrect implementation of W3C Content Security Policy. Under certain types of redirects Firefox incorrectly sets the source file to be the destination of the redirects. A remote attacker can gain knowledge of the destination URL.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Mozilla Firefox: 60.0 - 85.0.2

Firefox ESR: 60.0 - 60.9.0, 68.0 - 68.12.0, 78.0 - 78.7.1

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External links
https://www.mozilla.org/en-US/security/advisories/mfsa2021-07/
https://www.mozilla.org/en-US/security/advisories/mfsa2021-08/

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.