In MIT Kerberos 5 (aka krb5) before 1.22.3, there is a NULL pointer dereference if an application calls gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech. An unauthenticated remote attacker can trigger this, causing the process to terminate in parse_nego_message.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-1680 advisory.

    In MIT Kerberos 5 (aka krb5) before 1.22.3, there is a NULL pointer dereference if an application calls     gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech. An     unauthenticated remote attacker can trigger this, causing the process to terminate in parse_nego_message.
    (CVE-2026-40355)

    In MIT Kerberos 5 (aka krb5) before 1.22.3, there is an integer underflow and resultant out-of-bounds read     if an application calls gss_accept_sec_context() on a system with a NegoEx mechanism registered in     /etc/gss/mech. An unauthenticated remote attacker can trigger this, possibly causing the process to     terminate in parse_message. (CVE-2026-40356)

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 Redhat Enterprise Linux 9 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:19357 advisory.

    Kerberos is a network authentication system, which can improve the security of your network by eliminating     the insecure practice of sending passwords over the network in unencrypted form. It allows clients and     servers to authenticate to each other with the help of a trusted third party, the Kerberos key     distribution center (KDC).

    Security Fix(es):

    * krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read     (CVE-2026-40356)

    * krb5: MIT Kerberos 5: Denial of Service via NULL pointer dereference in NegoEx mechanism     (CVE-2026-40355)

    For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and     other related information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux 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 Redhat Enterprise Linux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:19145 advisory.

    Kerberos is a network authentication system, which can improve the security of your network by eliminating     the insecure practice of sending passwords over the network in unencrypted form. It allows clients and     servers to authenticate to each other with the help of a trusted third party, the Kerberos key     distribution center (KDC).

    Security Fix(es):

    * krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read     (CVE-2026-40356)

    * krb5: MIT Kerberos 5: Denial of Service via NULL pointer dereference in NegoEx mechanism     (CVE-2026-40355)

    For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and     other related information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux 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 RockyLinux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the RLSA-2026:16799 advisory.

    * krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read     (CVE-2026-40356)

    * krb5: MIT Kerberos 5: Denial of Service via NULL pointer dereference in NegoEx mechanism     (CVE-2026-40355)

Tenable has extracted the preceding description block directly from the RockyLinux 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 MiracleLinux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the AXSA:2026-613:03 advisory.

    * krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read     (CVE-2026-40356)
      * krb5: MIT Kerberos 5: Denial of Service via NULL pointer dereference in NegoEx mechanism     (CVE-2026-40355)

Tenable has extracted the preceding description block directly from the MiracleLinux 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 42 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-6c99aaa6d3 advisory.

    - Fix NegoEx parsing vulnerabilities (CVE-2026-40355, CVE-2026-40356)

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 Oracle Linux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the ELSA-2026-16799 advisory.

    [1.18.2-34.0.1]
    - Fixed race condition in krb5_set_password() [Orabug: 33609767]

    [1.18.2-34]
    - Fix NegoEx parsing vulnerabilities (CVE-2026-40355, CVE-2026-40356)       Resolves: RHEL-171589 RHEL-171594

Tenable has extracted the preceding description block directly from the Oracle Linux 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 AlmaLinux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the ALSA-2026:16799 advisory.

    * krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read     (CVE-2026-40356)
      * krb5: MIT Kerberos 5: Denial of Service via NULL pointer dereference in NegoEx mechanism     (CVE-2026-40355)

Tenable has extracted the preceding description block directly from the AlmaLinux 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 Redhat Enterprise Linux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:16799 advisory.

    Kerberos is a network authentication system, which can improve the security of your network by eliminating     the insecure practice of sending passwords over the network in unencrypted form. It allows clients and     servers to authenticate to each other with the help of a trusted third party, the Kerberos key     distribution center (KDC).

    Security Fix(es):

    * krb5: MIT Kerberos 5 (krb5): Denial of Service via integer underflow and out-of-bounds read     (CVE-2026-40356)

    * krb5: MIT Kerberos 5: Denial of Service via NULL pointer dereference in NegoEx mechanism     (CVE-2026-40355)

    For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and     other related information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux 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 a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-684396998a advisory.

    - Fix NegoEx parsing vulnerabilities (CVE-2026-40355, CVE-2026-40356)
    - Add upstream patches to build against openssl 4.0
    - Make configure.ac work with autoconf 2.73

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 CentOS Linux 9 host has packages installed that are affected by multiple vulnerabilities as referenced in the krb5-1.21.1-10.el9 build changelog.

  - In MIT Kerberos 5 (aka krb5) before 1.22.3, there is an integer underflow and resultant out-of-bounds read     if an application calls gss_accept_sec_context() on a system with a NegoEx mechanism registered in     /etc/gss/mech. An unauthenticated remote attacker can trigger this, possibly causing the process to     terminate in parse_message. (CVE-2026-40356)

  - In MIT Kerberos 5 (aka krb5) before 1.22.3, there is a NULL pointer dereference if an application calls     gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech. An     unauthenticated remote attacker can trigger this, causing the process to terminate in parse_nego_message.
    (CVE-2026-40355)

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 44 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-8b43ea2f82 advisory.

    * Fix NegoEx parsing vulnerabilities (CVE-2026-40355, CVE-2026-40356)
    * Add upstream patches to build against openssl 4.0
    * Make configure.ac work with autoconf 2.73

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 45 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-2e9fe57a46 advisory.

    Automatic update for krb5-1.22.2-7.fc45.

    ##### **Changelog**

    ```
    * Tue Apr 28 2026 Julien Rische <jrische@redhat.com> - 1.22.2-7
    - Fix NegoEx parsing vulnerabilities (CVE-2026-40355, CVE-2026-40356)
    - resolves: rhbz#2463398
    - resolves: rhbz#2463395

    ```

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

  - In MIT Kerberos 5 (aka krb5) before 1.22.3, there is a NULL pointer dereference if an application calls     gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech. An     unauthenticated remote attacker can trigger this, causing the process to terminate in parse_nego_message.
    (CVE-2026-40355)

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

ID	Name	Product	Family	Severity
315640	Amazon Linux 2023 : krb5-devel, krb5-libs, krb5-pkinit (ALAS2023-2026-1680)	Nessus	Amazon Linux Local Security Checks	medium
315480	RHEL 9 : krb5 (RHSA-2026:19357)	Nessus	Red Hat Local Security Checks	medium
315469	RHEL 10 : krb5 (RHSA-2026:19145)	Nessus	Red Hat Local Security Checks	medium
314682	RockyLinux 8 : krb5 (RLSA-2026:16799)	Nessus	Rocky Linux Local Security Checks	medium
314671	MiracleLinux 8 : krb5-1.18.2-34.el8_10 (AXSA:2026-613:03)	Nessus	Miracle Linux Local Security Checks	medium
314599	Fedora 42 : krb5 (2026-6c99aaa6d3)	Nessus	Fedora Local Security Checks	medium
314516	Oracle Linux 8 : krb5 (ELSA-2026-16799)	Nessus	Oracle Linux Local Security Checks	medium
314440	AlmaLinux 8 : krb5 (ALSA-2026:16799)	Nessus	Alma Linux Local Security Checks	medium
314391	RHEL 8 : krb5 (RHSA-2026:16799)	Nessus	Red Hat Local Security Checks	medium
312670	Fedora 43 : krb5 (2026-684396998a)	Nessus	Fedora Local Security Checks	medium
312105	CentOS 9 : krb5-1.21.1-10.el9	Nessus	CentOS Local Security Checks	medium
311728	Fedora 44 : krb5 (2026-8b43ea2f82)	Nessus	Fedora Local Security Checks	medium
311064	Fedora 45 : krb5 (2026-2e9fe57a46)	Nessus	Fedora Local Security Checks	medium
310811	Linux Distros Unpatched Vulnerability : CVE-2026-40355	Nessus	Misc.	medium

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