The version of Firefox installed on the remote macOS or Mac OS X host is prior to 88.0. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2021-16 advisory.

  - A WebGL framebuffer was not initialized early enough, resulting in memory corruption and an out of bound     write. (CVE-2021-23994)

  - When Responsive Design Mode was enabled, it used references to objects that were previously freed. We     presume that with enough effort this could have been exploited to run arbitrary code. (CVE-2021-23995)

  - By utilizing 3D CSS in conjunction with Javascript, content could have been rendered outside the webpage's     viewport, resulting in a spoofing attack that could have been used for phishing or other attacks on a     user. (CVE-2021-23996)

  - Due to unexpected data type conversions, a use-after-free could have occurred when interacting with the     font cache. We presume that with enough effort this could have been exploited to run arbitrary code.
    (CVE-2021-23997)

  - Through complicated navigations with new windows, an HTTP page could have inherited a secure lock icon     from an HTTPS page. (CVE-2021-23998)

  - If a Blob URL was loaded through some unusual user interaction, it could have been loaded by the System     Principal and granted additional privileges that should not be granted to web content. (CVE-2021-23999)

  - A race condition with requestPointerLock() and setTimeout() could have resulted     in a user interacting with one tab when they believed they were on a separate tab. In conjunction with     certain elements (such as <input type=file>) this could have led to an attack where a     user was confused about the origin of the webpage and potentially disclosed information they did not     intend to. (CVE-2021-24000)

  - A compromised content process could have performed session history manipulations it should not have been     able to due to testing infrastructure that was not restricted to testing-only configurations.
    (CVE-2021-24001)

  - When a user clicked on an FTP URL containing encoded newline characters (%0A and %0D), the newlines would     have been interpreted as such and allowed arbitrary commands to be sent to the FTP server.
    (CVE-2021-24002)

  - The WebAssembly JIT could miscalculate the size of a return type, which could lead to a null read and     result in a crash. Note: This issue only affected x86-32 platforms. Other platforms are unaffected.
    (CVE-2021-29945)

  - Lack of escaping allowed HTML injection when a webpage was viewed in Reader View. While a Content Security     Policy prevents direct code execution, HTML injection is still possible.Note: This issue only affected     Firefox for Android. Other operating systems are unaffected. (CVE-2021-29944)

  - Ports that were written as an integer overflow above the bounds of a 16-bit integer could have bypassed     port blocking restrictions when used in the Alt-Svc header. (CVE-2021-29946)

  - Mozilla developers and community members Ryan VanderMeulen, Sean Feng, Tyson Smith, Julian Seward,     Christian Holler reported memory safety bugs present in Firefox 87. Some of these bugs showed evidence of     memory corruption and we presume that with enough effort some of these could have been exploited to run     arbitrary code. (CVE-2021-29947)

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

The remote Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-4926-1 advisory.

    Multiple security issues were discovered in Firefox. If a user were tricked into opening a specially     crafted website, an attacker could potentially exploit these to cause a denial of service, spoof the     browser UI, bypass security restrictions, trick the user into disclosing confidential information, or     execute arbitrary code. (CVE-2021-23994, CVE-2021-23996, CVE-2021-23997, CVE-2021-23998, CVE-2021-23999,     CVE-2021-24000, CVE-2021-24001, CVE-2021-29945, CVE-2021-29946, CVE-2021-29947)

    A use-after-free was discovered when Responsive Design Mode was enabled. If a user were tricked into     opening a specially crafted website with Responsive Design Mode enabled, an attacker could potentially     exploit this to cause a denial of service, or execute arbitrary code. (CVE-2021-23995)

    It was discovered that Firefox mishandled ftp URLs with encoded newline characters. If a user were tricked     into clicking on a specially crafted link, an attacker could potentially exploit this to send arbitrary     FTP commands. (CVE-2021-24002)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

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

The version of Firefox installed on the remote Windows host is prior to 88.0. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2021-16 advisory.

  - A WebGL framebuffer was not initialized early enough, resulting in memory corruption and an out of bound     write. (CVE-2021-23994)

  - When Responsive Design Mode was enabled, it used references to objects that were previously freed. We     presume that with enough effort this could have been exploited to run arbitrary code. (CVE-2021-23995)

  - By utilizing 3D CSS in conjunction with Javascript, content could have been rendered outside the webpage's     viewport, resulting in a spoofing attack that could have been used for phishing or other attacks on a     user. (CVE-2021-23996)

  - Due to unexpected data type conversions, a use-after-free could have occurred when interacting with the     font cache. We presume that with enough effort this could have been exploited to run arbitrary code.
    (CVE-2021-23997)

  - Through complicated navigations with new windows, an HTTP page could have inherited a secure lock icon     from an HTTPS page. (CVE-2021-23998)

  - If a Blob URL was loaded through some unusual user interaction, it could have been loaded by the System     Principal and granted additional privileges that should not be granted to web content. (CVE-2021-23999)

  - A race condition with requestPointerLock() and setTimeout() could have resulted     in a user interacting with one tab when they believed they were on a separate tab. In conjunction with     certain elements (such as <input type=file>) this could have led to an attack where a     user was confused about the origin of the webpage and potentially disclosed information they did not     intend to. (CVE-2021-24000)

  - A compromised content process could have performed session history manipulations it should not have been     able to due to testing infrastructure that was not restricted to testing-only configurations.
    (CVE-2021-24001)

  - When a user clicked on an FTP URL containing encoded newline characters (%0A and %0D), the newlines would     have been interpreted as such and allowed arbitrary commands to be sent to the FTP server.
    (CVE-2021-24002)

  - The WebAssembly JIT could miscalculate the size of a return type, which could lead to a null read and     result in a crash. Note: This issue only affected x86-32 platforms. Other platforms are unaffected.
    (CVE-2021-29945)

  - Lack of escaping allowed HTML injection when a webpage was viewed in Reader View. While a Content Security     Policy prevents direct code execution, HTML injection is still possible.Note: This issue only affected     Firefox for Android. Other operating systems are unaffected. (CVE-2021-29944)

  - Ports that were written as an integer overflow above the bounds of a 16-bit integer could have bypassed     port blocking restrictions when used in the Alt-Svc header. (CVE-2021-29946)

  - Mozilla developers and community members Ryan VanderMeulen, Sean Feng, Tyson Smith, Julian Seward,     Christian Holler reported memory safety bugs present in Firefox 87. Some of these bugs showed evidence of     memory corruption and we presume that with enough effort some of these could have been exploited to run     arbitrary code. (CVE-2021-29947)

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

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - By utilizing 3D CSS in conjunction with Javascript, content could have been rendered outside the webpage's     viewport, resulting in a spoofing attack that could have been used for phishing or other attacks on a     user. This vulnerability affects Firefox < 88. (CVE-2021-23996)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Published	Updated	Severity
148766	Mozilla Firefox < 88.0	Nessus	MacOS X Local Security Checks	4/19/2021	1/3/2024	high
148992	Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS : Firefox vulnerabilities (USN-4926-1)	Nessus	Ubuntu Local Security Checks	4/26/2021	8/28/2024	high
148767	Mozilla Firefox < 88.0	Nessus	Windows	4/19/2021	1/3/2024	high
244601	Linux Distros Unpatched Vulnerability : CVE-2021-23996	Nessus	Misc.	8/7/2025	8/7/2025	medium

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