When a user explicitly requested Thunderbird to decrypt an inline OpenPGP message that was embedded in a text section of an email that was formatted and styled with HTML and CSS, then the decrypted contents were rendered in a context in which the CSS styles from the outer messages were active. If the user had additionally allowed loading of the remote content referenced by the outer email message, and the email was crafted by the sender using a combination of CSS rules and fonts and animations, then it was possible to extract the secret contents of the email. This vulnerability affects Thunderbird < 147.0.1 and Thunderbird < 140.7.1.

The version of thunderbird installed on the remote host is prior to 140.7.1-1. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2026-3167 advisory.

    Spoofing issue in the Downloads Panel component. This vulnerability affects Firefox < 146.
    (CVE-2025-14327)

    CSS-based exfiltration of the content from partially encrypted emails when allowing remote content. This     vulnerability affects Thunderbird < 147.0.1 and Thunderbird < 140.7.1. (CVE-2026-0818)

    Mitigation bypass in the DOM: Security component. This vulnerability affects Firefox < 147, Firefox ESR <     115.32, and Firefox ESR < 140.7. (CVE-2026-0877)

    Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component. This     vulnerability affects Firefox < 147 and Firefox ESR < 140.7. (CVE-2026-0878)

    Sandbox escape due to incorrect boundary conditions in the Graphics component. This vulnerability affects     Firefox < 147, Firefox ESR < 115.32, and Firefox ESR < 140.7. (CVE-2026-0879)

    Sandbox escape due to integer overflow in the Graphics component. This vulnerability affects Firefox <     147, Firefox ESR < 115.32, and Firefox ESR < 140.7. (CVE-2026-0880)

    Use-after-free in the IPC component. This vulnerability affects Firefox < 147, Firefox ESR < 115.32, and     Firefox ESR < 140.7. (CVE-2026-0882)

    Information disclosure in the Networking component. This vulnerability affects Firefox < 147 and Firefox     ESR < 140.7. (CVE-2026-0883)

    Use-after-free in the JavaScript Engine component. This vulnerability affects Firefox < 147 and Firefox     ESR < 140.7. (CVE-2026-0884)

    Use-after-free in the JavaScript: GC component. This vulnerability affects Firefox < 147 and Firefox ESR <     140.7. (CVE-2026-0885)

    Incorrect boundary conditions in the Graphics component. This vulnerability affects Firefox < 147, Firefox     ESR < 115.32, and Firefox ESR < 140.7. (CVE-2026-0886)

    Clickjacking issue, information disclosure in the PDF Viewer component. This vulnerability affects Firefox     < 147 and Firefox ESR < 140.7. (CVE-2026-0887)

    Spoofing issue in the DOM: Copy & Paste and Drag & Drop component. This vulnerability affects Firefox <     147 and Firefox ESR < 140.7. (CVE-2026-0890)

    Memory safety bugs present in Firefox ESR 140.6, Thunderbird ESR 140.6, Firefox 146 and Thunderbird 146.
    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. This vulnerability affects Firefox < 147 and     Firefox ESR < 140.7. (CVE-2026-0891)

Tenable has extracted the preceding description block directly from the tested product 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 SUSE Linux SLED15 / SLED_SAP15 / SLES15 / SLES_SAP15 / openSUSE 15 host has packages installed that are affected by a vulnerability as referenced in the SUSE-SU-2026:0388-1 advisory.

    Update to Mozilla Thunderbird 140.7.1 MFSA 2026-08 (bsc#1257397):

    - CVE-2026-0818: CSS-based exfiltration of the content from partially encrypted emails when allowing     remote content

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

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

The remote Debian 11 host has packages installed that are affected by a vulnerability as referenced in the dla-4466 advisory.

    - -------------------------------------------------------------------------     Debian LTS Advisory DLA-4466-1                debian-lts@lists.debian.org     https://www.debian.org/lts/security/               Emilio Pozuelo Monfort     February 04, 2026                             https://wiki.debian.org/LTS
    - -------------------------------------------------------------------------

    Package        : thunderbird     Version        : 1:140.7.1esr-1~deb11u1     CVE ID         : CVE-2026-0818

    A security issue was discovered in Thunderbird, which could result in     information disclosure.

    For Debian 11 bullseye, this problem has been fixed in version     1:140.7.1esr-1~deb11u1.

    We recommend that you upgrade your thunderbird packages.

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

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

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

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

The remote Debian 12 / 13 host has packages installed that are affected by a vulnerability as referenced in the dsa-6118 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6118-1                   security@debian.org     https://www.debian.org/security/                       Moritz Muehlenhoff     February 03, 2026                     https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : thunderbird     CVE ID         : CVE-2026-0818

    A security issue was discovered in Thunderbird, which could result in     information disclosure

    For the oldstable distribution (bookworm), this problem has been fixed     in version 1:140.7.1esr-1~deb12u1.

    For the stable distribution (trixie), this problem has been fixed in     version 1:140.7.1esr-1~deb13u1.

    We recommend that you upgrade your thunderbird packages.

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

    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 this issue but has instead relied only on the application's self-reported version number.

The remote Ubuntu 22.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-7991-1 advisory.

    Multiple security issues were discovered in Thunderbird. If a user were tricked into opening a specially     crafted website in a browsing context, an attacker could potentially exploit these to cause a denial of     service, obtain sensitive information, bypass security restrictions, cross-site tracing, or execute     arbitrary code.

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 Thunderbird installed on the remote macOS or Mac OS X host is prior to 147.0.1. It is, therefore, affected by a vulnerability as referenced in the mfsa2026-07 advisory.

  - When a user explicitly requested Thunderbird to decrypt an inline OpenPGP message that was embedded in a     text section of an email that was formatted and styled with HTML and CSS, then the decrypted contents were     rendered in a context in which the CSS styles from the outer messages were active. If the user had     additionally allowed loading of the remote content referenced by the outer email message, and the email     was crafted by the sender using a combination of CSS rules and fonts and animations, then it was possible     to extract the secret contents of the email. (CVE-2026-0818)

Note that Nessus has not tested for this issue 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 140.7.1. It is, therefore, affected by a vulnerability as referenced in the mfsa2026-08 advisory.

  - When a user explicitly requested Thunderbird to decrypt an inline OpenPGP message that was embedded in a     text section of an email that was formatted and styled with HTML and CSS, then the decrypted contents were     rendered in a context in which the CSS styles from the outer messages were active. If the user had     additionally allowed loading of the remote content referenced by the outer email message, and the email     was crafted by the sender using a combination of CSS rules and fonts and animations, then it was possible     to extract the secret contents of the email. (CVE-2026-0818)

Note that Nessus has not tested for this issue 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 140.7.1. It is, therefore, affected by a vulnerability as referenced in the mfsa2026-08 advisory.

  - When a user explicitly requested Thunderbird to decrypt an inline OpenPGP message that was embedded in a     text section of an email that was formatted and styled with HTML and CSS, then the decrypted contents were     rendered in a context in which the CSS styles from the outer messages were active. If the user had     additionally allowed loading of the remote content referenced by the outer email message, and the email     was crafted by the sender using a combination of CSS rules and fonts and animations, then it was possible     to extract the secret contents of the email. (CVE-2026-0818)

Note that Nessus has not tested for this issue 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 147.0.1. It is, therefore, affected by a vulnerability as referenced in the mfsa2026-07 advisory.

  - When a user explicitly requested Thunderbird to decrypt an inline OpenPGP message that was embedded in a     text section of an email that was formatted and styled with HTML and CSS, then the decrypted contents were     rendered in a context in which the CSS styles from the outer messages were active. If the user had     additionally allowed loading of the remote content referenced by the outer email message, and the email     was crafted by the sender using a combination of CSS rules and fonts and animations, then it was possible     to extract the secret contents of the email. (CVE-2026-0818)

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

ID	Name	Product	Family	Severity
299518	Amazon Linux 2 : thunderbird, --advisory ALAS2-2026-3167 (ALAS-2026-3167)	Nessus	Amazon Linux Local Security Checks	high
298234	SUSE SLED15 / SLES15 / openSUSE 15 Security Update : MozillaThunderbird (SUSE-SU-2026:0388-1)	Nessus	SuSE Local Security Checks	medium
297821	Debian dla-4466 : thunderbird - security update	Nessus	Debian Local Security Checks	medium
297740	Debian dsa-6118 : thunderbird - security update	Nessus	Debian Local Security Checks	medium
297659	Ubuntu 22.04 LTS : Thunderbird vulnerabilities (USN-7991-1)	Nessus	Ubuntu Local Security Checks	medium
297035	Mozilla Thunderbird < 147.0.1	Nessus	MacOS X Local Security Checks	medium
297034	Mozilla Thunderbird < 140.7.1	Nessus	MacOS X Local Security Checks	medium
297033	Mozilla Thunderbird < 140.7.1	Nessus	Windows	medium
297032	Mozilla Thunderbird < 147.0.1	Nessus	Windows	medium

Detections

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CVE-2026-0818

medium

Tenable Plugins

high

medium

medium

medium

medium

medium

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medium