In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8 trailing characters are present (malformed UTF-8 header data). Information might be divulged within an error message produced during handling of an unrelated e-mail message.

The remote Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8382-1 advisory.

    Timo Longin discovered that Exim incorrectly handled certain SMTP messages in PIPELINING/CHUNKING     configurations. A remote attacker could possibly use this issue to perform SMTP smuggling. This issue only     affected Ubuntu 14.04 LTS. (CVE-2023-51766)

    It was discovered that Exim incorrectly handled certain malformed JSON data in headers. A remote attacker     could possibly use this issue to crash Exim, resulting in a denial of service, or execute arbitrary code.
    This issue only affected Ubuntu 20.04 LTS. (CVE-2026-40685)

    It was discovered that Exim incorrectly handled certain malformed UTF-8 headers. A remote attacker could     possibly use this issue to obtain sensitive information. This issue only affected Ubuntu 20.04 LTS.
    (CVE-2026-40686)

    It was discovered that Exim incorrectly handled certain SPA resources. A remote attacker could possibly     use this issue to crash Exim, resulting in a denial of service, or obtain sensitive information. This     issue only affected Ubuntu 20.04 LTS. (CVE-2026-40687)

    It was discovered that Exim incorrectly handled certain CHUNKING transfers in some GnuTLS configurations.
    A remote attacker could possibly use this issue to crash Exim, resulting in a denial of service, or     execute arbitrary code. This issue only affected Ubuntu 20.04 LTS. (CVE-2026-45185)

    Warisjeet Singh discovered that Exim incorrectly handled certain proxy connections in builds with proxy     support enabled. A remote attacker could possibly use this issue to obtain sensitive information. This     issue only affected Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, and Ubuntu 20.04 LTS. (CVE-2026-48840)

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 remote Debian 12 / 13 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-6265 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6265-1                   security@debian.org     https://www.debian.org/security/                     Salvatore Bonaccorso     May 12, 2026                          https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : exim4     CVE ID         : CVE-2026-40684 CVE-2026-40685 CVE-2026-40686 CVE-2026-40687

    Several vulnerabilities were discovered in the Exim mail transport     agent, which may result in remote code execution, denial of service or     an information leak.

    For the oldstable distribution (bookworm), these problems have been fixed     in version 4.96-15+deb12u9.

    For the stable distribution (trixie), these problems have been fixed in     version 4.98.2-1+deb13u2.

    We recommend that you upgrade your exim4 packages.

    For the detailed security status of exim4 please refer to its security     tracker page at:
    https://security-tracker.debian.org/tracker/exim4

    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 remote Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8228-1 advisory.

    It was discovered that Exim incorrectly handled parsing malformed JSON in message headers. A remote     attacker could possibly use this issue to execute arbitrary code. (CVE-2026-40685)

    It was discovered that Exim incorrectly handled processing of UTF-8 trailing characters. A remote attacker     could possibly use this issue to obtain sensitive information. (CVE-2026-40686)

    It was discovered that Exim incorrectly handled SPA authenticator input. An authenticated user could     possibly use this issue to execute arbitrary code. (CVE-2026-40687)

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

  - In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8     trailing characters are present (malformed UTF-8 header data). Information might be divulged within an     error message produced during handling of an unrelated e-mail message. (CVE-2026-40686)

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

ID	Name	Product	Family	Severity
318625	Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS : Exim vulnerabilities (USN-8382-1)	Nessus	Ubuntu Local Security Checks	critical
314336	Debian dsa-6265 : exim4 - security update	Nessus	Debian Local Security Checks	critical
312296	Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS : Exim vulnerabilities (USN-8228-1)	Nessus	Ubuntu Local Security Checks	critical
311151	Linux Distros Unpatched Vulnerability : CVE-2026-40686	Nessus	Misc.	medium

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CVE-2026-40686

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