The version of Firefox installed on the remote macOS or Mac OS X host is prior to 155.0. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-82 advisory.

  - Privilege escalation due to invalid pointer in the Graphics component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-84131)

  - Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-84121)

  - Use-after-free in the JavaScript: GC component. This vulnerability was fixed in Firefox 155 and Firefox     ESR 153.2. (CVE-2026-84118)

  - Sandbox escape due to use-after-free in the DOM: Navigation component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-84119)

  - Use-after-free in the Audio/Video component. This vulnerability was fixed in Firefox 155, Firefox ESR     115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-84120)

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 Thunderbird installed on the remote Windows host is prior to 155.0. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-86 advisory.

  - Privilege escalation due to invalid pointer in the Graphics component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird     140.15, and Thunderbird 153.2. (CVE-2026-84131)

  - Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird     140.15, and Thunderbird 153.2. (CVE-2026-84121)

  - Triggering an error condition in certain MIME bodies would cause uninitialized memory to be used.
    (CVE-2026-84639)

  - A maliciously constructed mail header could lead to a one byte read past the end of a buffer.
    (CVE-2026-84640)

  - A malicious IMAP server can trigger use-after-free and heap-memory disclosure by sending a crafted ID     response. Heap contents can ultimately be persisted to prefs.js. (CVE-2026-84641)

Note that Nessus has not tested for these issues 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.

  - Internally found bugs present in Thunderbird 154. Some of these bugs showed evidence of memory corruption     or another security-relevant defect and we presume that with enough effort some of these could have been     exploited. This vulnerability was fixed in Firefox 155 and Thunderbird 155. (CVE-2026-84142)

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

The version of Firefox installed on the remote Windows host is prior to 155.0. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-82 advisory.

  - Privilege escalation due to invalid pointer in the Graphics component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-84131)

  - Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-84121)

  - Use-after-free in the JavaScript: GC component. This vulnerability was fixed in Firefox 155 and Firefox     ESR 153.2. (CVE-2026-84118)

  - Sandbox escape due to use-after-free in the DOM: Navigation component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-84119)

  - Use-after-free in the Audio/Video component. This vulnerability was fixed in Firefox 155, Firefox ESR     115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-84120)

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 Thunderbird installed on the remote macOS or Mac OS X host is prior to 155.0. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-86 advisory.

  - Privilege escalation due to invalid pointer in the Graphics component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird     140.15, and Thunderbird 153.2. (CVE-2026-84131)

  - Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in     Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird     140.15, and Thunderbird 153.2. (CVE-2026-84121)

  - Triggering an error condition in certain MIME bodies would cause uninitialized memory to be used.
    (CVE-2026-84639)

  - A maliciously constructed mail header could lead to a one byte read past the end of a buffer.
    (CVE-2026-84640)

  - A malicious IMAP server can trigger use-after-free and heap-memory disclosure by sending a crafted ID     response. Heap contents can ultimately be persisted to prefs.js. (CVE-2026-84641)

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

ID	Name	Product	Family	Published	Updated	Severity
342201	Mozilla Firefox < 155.0	Nessus	MacOS X Local Security Checks	9/1/2026	9/1/2026	critical
342256	Mozilla Thunderbird < 155.0	Nessus	Windows	9/1/2026	9/1/2026	critical
342297	Linux Distros Unpatched Vulnerability : CVE-2026-84142	Nessus	Misc.	9/2/2026	9/2/2026	critical
342204	Mozilla Firefox < 155.0	Nessus	Windows	9/1/2026	9/1/2026	critical
342261	Mozilla Thunderbird < 155.0	Nessus	MacOS X Local Security Checks	9/1/2026	9/1/2026	critical

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