Detections
Analytics

Mozilla Firefox ESR < 91.3

critical Nessus Plugin ID 154816

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Synopsis

A web browser installed on the remote macOS or Mac OS X host is affected by multiple vulnerabilities.

Description

The version of Firefox ESR installed on the remote macOS or Mac OS X host is prior to 91.3. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2021-49 advisory.

 - The iframe sandbox rules were not correctly applied to XSLT stylesheets, allowing an iframe to bypass restrictions such as executing scripts or navigating the top-level frame. (CVE-2021-38503)

 - When interacting with an HTML input element's file picker dialog with <code>webkitdirectory</code> set, a use-after-free could have resulted, leading to memory corruption and a potentially exploitable crash.
 (CVE-2021-38504)

 - Microsoft introduced a new feature in Windows 10 known as Cloud Clipboard which, if enabled, will record data copied to the clipboard to the cloud, and make it available on other computers in certain scenarios.
 Applications that wish to prevent copied data from being recorded in Cloud History must use specific clipboard formats; and Firefox before versions 94 and ESR 91.3 did not implement them. This could have caused sensitive data to be recorded to a user's Microsoft account. This bug only affects Firefox for Windows 10+ with Cloud Clipboard enabled. Other operating systems are unaffected. (CVE-2021-38505)

 - Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning to the user. This could lead to spoofing attacks on the browser UI including phishing.
 (CVE-2021-38506)

 - The Opportunistic Encryption feature of HTTP2 (RFC 8164) allows a connection to be transparently upgraded to TLS while retaining the visual properties of an HTTP connection, including being same-origin with unencrypted connections on port 80. However, if a second encrypted port on the same IP address (e.g. port 8443) did not opt-in to opportunistic encryption; a network attacker could forward a connection from the browser to port 443 to port 8443, causing the browser to treat the content of port 8443 as same-origin with HTTP. This was resolved by disabling the Opportunistic Encryption feature, which had low usage.
 (CVE-2021-38507)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Upgrade to Mozilla Firefox ESR version 91.3 or later.

See Also

https://www.mozilla.org/en-US/security/advisories/mfsa2021-49/

Plugin Details

Severity: Critical

ID: 154816

File Name: macos_firefox_91_3_esr.nasl

Version: 1.8

Type: local

Agent: macosx

Published: 11/2/2021

Updated: 11/18/2025

Supported Sensors: Frictionless Assessment Agent, Frictionless Assessment AWS, Frictionless Assessment Azure, Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: High

Score: 7.3

CVSS v2

Risk Factor: High

Base Score: 7.5

Temporal Score: 5.5

Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS Score Source: CVE-2021-38503

CVSS v3

Risk Factor: Critical

Base Score: 10

Temporal Score: 8.7

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/a:mozilla:firefox_esr

Required KB Items: installed_sw/Mozilla Firefox ESR

Exploit Ease: No known exploits are available

Patch Publication Date: 11/2/2021

Vulnerability Publication Date: 11/2/2021

Reference Information

CVE: CVE-2021-38503, CVE-2021-38504, CVE-2021-38505, CVE-2021-38506, CVE-2021-38507, CVE-2021-38508, CVE-2021-38509, CVE-2021-38510, CVE-2021-43534, CVE-2021-43535

IAVA: 2021-A-0527-S