Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. 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, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

The remote Fedora 44 host has packages installed that are affected by multiple vulnerabilities as referenced in the FEDORA-2026-42a3a95e62 advisory.

    NSS Release Notes

    Update NSS to 3.127.0

    - Bug 1869493 - Heap-buffer overflow in AES Keywrap.
    - Bug 2052210 - Generate additional test message for Thunderbird (HTML with remote image).
    - Bug 2052709 - Convert NSS 3.126 release notes to Markdown.
    - Bug 2053831 - clang format.
    - Bug 2054609 - remove cipher suite order exception from bug 946147.
    - Bug 2054714 - avoid leaking stale ECH outer extensions across HRR.
    - Bug 2054719 - fix content type tag for CMS AuthEnvelopedData plaintext.
    - Bug 2056291 - remove support for pre-v1.0 PKCS#12.
    - Bug 2056846 - Remove unused policy string callback to fix -Wunused-but-set-global.
    - Bug 2057184 - Enable -Wunused-but-set-variable/-global in werror.py.
    - Bug 2059176 - EC_DerivePublicKey() failure is not propagated in sftk_mkPrivKey().
    - Bug 2060118 - remove DH_GenParam support.
    - Bug 2060720 - Round ECH ClientHelloInner padding up to a multiple of 32.
    - Bug 2061107 - restore pkcs12.h for source compatibility.
    - Bug 2063071 - make selfserv listen on IPv6 wildcard on dual-stack hosts.

    https://firefox-source-docs.mozilla.org/security/nss/releases/nss_3_127.html

    - Updated Firefox to latest release (155.0)

Tenable has extracted the preceding description block directly from the Fedora 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 remote Fedora 43 host has packages installed that are affected by multiple vulnerabilities as referenced in the FEDORA-2026-208add2041 advisory.

    NSS Release Notes

    Update NSS to 3.127.0

    - Bug 1869493 - Heap-buffer overflow in AES Keywrap.
    - Bug 2052210 - Generate additional test message for Thunderbird (HTML with remote image).
    - Bug 2052709 - Convert NSS 3.126 release notes to Markdown.
    - Bug 2053831 - clang format.
    - Bug 2054609 - remove cipher suite order exception from bug 946147.
    - Bug 2054714 - avoid leaking stale ECH outer extensions across HRR.
    - Bug 2054719 - fix content type tag for CMS AuthEnvelopedData plaintext.
    - Bug 2056291 - remove support for pre-v1.0 PKCS#12.
    - Bug 2056846 - Remove unused policy string callback to fix -Wunused-but-set-global.
    - Bug 2057184 - Enable -Wunused-but-set-variable/-global in werror.py.
    - Bug 2059176 - EC_DerivePublicKey() failure is not propagated in sftk_mkPrivKey().
    - Bug 2060118 - remove DH_GenParam support.
    - Bug 2060720 - Round ECH ClientHelloInner padding up to a multiple of 32.
    - Bug 2061107 - restore pkcs12.h for source compatibility.
    - Bug 2063071 - make selfserv listen on IPv6 wildcard on dual-stack hosts.

    https://firefox-source-docs.mozilla.org/security/nss/releases/nss_3_127.html

    - Updated Firefox to latest upstream (155.0)

Tenable has extracted the preceding description block directly from the Fedora 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 remote Debian 13 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-6481 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6481-1                   security@debian.org     https://www.debian.org/security/                       Moritz Muehlenhoff     September 02, 2026                    https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : firefox-esr     CVE ID         : CVE-2026-16365 CVE-2026-16371 CVE-2026-75874 CVE-2026-84119                      CVE-2026-84120 CVE-2026-84121 CVE-2026-84122 CVE-2026-84124                      CVE-2026-84131 CVE-2026-84143 CVE-2026-84145

    Multiple security issues have been found in the Mozilla Firefox web     browser, which could potentially result in the execution of arbitrary     code, sandbox escape or privilege escalation.

    For the stable distribution (trixie), these problems have been fixed in     version 140.15.0esr-1~deb13u1.

    We recommend that you upgrade your firefox-esr packages.

    For the detailed security status of firefox-esr please refer to     its security tracker page at:
    https://security-tracker.debian.org/tracker/firefox-esr

    Further information about Debian Security Advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://www.debian.org/security/

    Mailing list: debian-security-announce@lists.debian.org

Tenable has extracted the preceding description block directly from the Debian 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 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, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. 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,     Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
    (CVE-2026-84143)

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

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.

The version of Thunderbird installed on the remote macOS or Mac OS X host is prior to 153.2. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-88 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 in the Remote Settings Client component. This vulnerability was fixed in Firefox 154,     Thunderbird 154, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 140.15, and     Thunderbird 153.2. (CVE-2026-75874)

  - 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 version of Thunderbird installed on the remote Windows host is prior to 153.2. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-88 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 in the Remote Settings Client component. This vulnerability was fixed in Firefox 154,     Thunderbird 154, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 140.15, and     Thunderbird 153.2. (CVE-2026-75874)

  - 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 version of Thunderbird installed on the remote Windows host is prior to 140.15. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-87 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 in the Remote Settings Client component. This vulnerability was fixed in Firefox 154,     Thunderbird 154, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 140.15, and     Thunderbird 153.2. (CVE-2026-75874)

  - 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 version of Thunderbird installed on the remote macOS or Mac OS X host is prior to 140.15. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-87 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 in the Remote Settings Client component. This vulnerability was fixed in Firefox 154,     Thunderbird 154, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 140.15, and     Thunderbird 153.2. (CVE-2026-75874)

  - 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 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 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 Firefox ESR installed on the remote macOS or Mac OS X host is prior to 153.2. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-85 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 in the Remote Settings Client component. This vulnerability was fixed in Firefox 154,     Thunderbird 154, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-75874)

  - 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 Firefox ESR installed on the remote Windows host is prior to 153.2. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-85 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 in the Remote Settings Client component. This vulnerability was fixed in Firefox 154,     Thunderbird 154, Firefox ESR 115.40, Firefox ESR 140.15, and Firefox ESR 153.2. (CVE-2026-75874)

  - 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 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 Firefox ESR installed on the remote macOS or Mac OS X host is prior to 140.15. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-84 advisory.

  - Sandbox escape in the Remote Settings Client component. This vulnerability was fixed in Firefox 154 and     Thunderbird 154. (CVE-2026-75874)

  - Privilege escalation in the DOM: Workers component. This vulnerability was fixed in Firefox 153,     Thunderbird 153, and Firefox ESR 140.15. (CVE-2026-16365)

  - 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)

  - Use-after-free in the Audio/Video component. This vulnerability was fixed in Firefox 155, Firefox ESR     140.15, and Firefox ESR 153.2. (CVE-2026-84122)

  - Privilege escalation in the DOM: Navigation component. This vulnerability was fixed in Firefox 153,     Firefox ESR 140.13, Thunderbird 153, Thunderbird 140.13, and Firefox ESR 140.15. (CVE-2026-16371)

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 ESR installed on the remote Windows host is prior to 140.15. It is, therefore, affected by multiple vulnerabilities as referenced in the mfsa2026-84 advisory.

  - Sandbox escape in the Remote Settings Client component. This vulnerability was fixed in Firefox 154 and     Thunderbird 154. (CVE-2026-75874)

  - Privilege escalation in the DOM: Workers component. This vulnerability was fixed in Firefox 153,     Thunderbird 153, and Firefox ESR 140.15. (CVE-2026-16365)

  - 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)

  - Use-after-free in the Audio/Video component. This vulnerability was fixed in Firefox 155, Firefox ESR     140.15, and Firefox ESR 153.2. (CVE-2026-84122)

  - Privilege escalation in the DOM: Navigation component. This vulnerability was fixed in Firefox 153,     Firefox ESR 140.13, Thunderbird 153, Thunderbird 140.13, and Firefox ESR 140.15. (CVE-2026-16371)

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	Type	Severity
342567	Fedora 44 : firefox / nss (2026-42a3a95e62)	Nessus	Fedora Local Security Checks	Local	critical
342518	Fedora 43 : firefox / nss (2026-208add2041)	Nessus	Fedora Local Security Checks	Local	critical
342446	Debian dsa-6481 : firefox-esr - security update	Nessus	Debian Local Security Checks	Local	critical
342306	Linux Distros Unpatched Vulnerability : CVE-2026-84143	Nessus	Misc.	Local	high
342261	Mozilla Thunderbird < 155.0	Nessus	MacOS X Local Security Checks	Local	critical
342260	Mozilla Thunderbird < 153.2	Nessus	MacOS X Local Security Checks	Local	critical
342259	Mozilla Thunderbird < 153.2	Nessus	Windows	Local	critical
342258	Mozilla Thunderbird < 140.15	Nessus	Windows	Local	critical
342257	Mozilla Thunderbird < 140.15	Nessus	MacOS X Local Security Checks	Local	critical
342256	Mozilla Thunderbird < 155.0	Nessus	Windows	Local	critical
342204	Mozilla Firefox < 155.0	Nessus	Windows	Local	critical
342203	Mozilla Firefox ESR < 153.2	Nessus	MacOS X Local Security Checks	Local	critical
342202	Mozilla Firefox ESR < 153.2	Nessus	Windows	Local	critical
342201	Mozilla Firefox < 155.0	Nessus	MacOS X Local Security Checks	Local	critical
342132	Mozilla Firefox ESR < 140.15	Nessus	MacOS X Local Security Checks	Local	critical
342131	Mozilla Firefox ESR < 140.15	Nessus	Windows	Local	critical

Detections

Analytics

CVE-2026-84143

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Tenable Plugins

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