A flaw was found in libssh. On servers with GSSAPIKeyExchange enabled, the gssapi-keyex path does not verify whether the authenticated Kerberos principal is authorized for the requested local user, allowing authenticated clients to log in as arbitrary users.

The remote AlmaLinux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the ALSA-2026:55855 advisory.

    * libssh: libssh: information disclosure via short GSSAPI Curve25519 public key (CVE-2026-59842)
      * libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)
      * libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)
      * libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)
      * libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)
      * libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)
      * libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)
      * libssh: libssh: denial of service via automatic certificate authentication loop (CVE-2026-59849)
      * libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)
      * libssh: libssh: authentication bypass via missing GSSAPI principal check (CVE-2026-59851)
      * libssh: libssh: stack buffer overflow in SFTP server longname construction (CVE-2026-15370)

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 RockyLinux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the RLSA-2026:55855 advisory.

    * libssh: libssh: information disclosure via short GSSAPI Curve25519 public key (CVE-2026-59842)

    * libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)

    * libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)

    * libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)

    * libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)

    * libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)

    * libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)

    * libssh: libssh: denial of service via automatic certificate authentication loop (CVE-2026-59849)

    * libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)

    * libssh: libssh: authentication bypass via missing GSSAPI principal check (CVE-2026-59851)

    * libssh: libssh: stack buffer overflow in SFTP server longname construction (CVE-2026-15370)

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 Redhat Enterprise Linux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:55855 advisory.

    libssh is a library which implements the SSH protocol. It can be used to implement client and server     applications.

    Security Fix(es):

    * libssh: libssh: information disclosure via short GSSAPI Curve25519 public key (CVE-2026-59842)

    * libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)

    * libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)

    * libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)

    * libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)

    * libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)

    * libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)

    * libssh: libssh: denial of service via automatic certificate authentication loop (CVE-2026-59849)

    * libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)

    * libssh: libssh: authentication bypass via missing GSSAPI principal check (CVE-2026-59851)

    * libssh: libssh: stack buffer overflow in SFTP server longname construction (CVE-2026-15370)

    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 Oracle Linux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the ELSA-2026-55855 advisory.

    [0.12.0-3]
    - Backport CVE fixes from 0.12.2       Resolves: RHEL-213004       Resolves: RHEL-213029       Resolves: RHEL-213032       Resolves: RHEL-213039       Resolves: RHEL-213046       Resolves: RHEL-213079       Resolves: RHEL-213112       Resolves: RHEL-213117       Resolves: RHEL-213148       Resolves: RHEL-213150       Resolves: RHEL-213175

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

  - A flaw was found in libssh. On servers with GSSAPIKeyExchange enabled, the gssapi-keyex path does not     verify whether the authenticated Kerberos principal is authorized for the requested local user, allowing     authenticated clients to log in as arbitrary users. (CVE-2026-59851)

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

The remote Fedora 44 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-0e46c91ccf advisory.

    New upstream security release


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.

ID	Name	Product	Family	Type	Severity
337665	AlmaLinux 10 : libssh (ALSA-2026:55855)	Nessus	Alma Linux Local Security Checks	Local	high
337638	RockyLinux 10 : libssh (RLSA-2026:55855)	Nessus	Rocky Linux Local Security Checks	Local	high
337346	RHEL 10 : libssh (RHSA-2026:55855)	Nessus	Red Hat Local Security Checks	Local	high
337118	Oracle Linux 10 : libssh (ELSA-2026-55855)	Nessus	Oracle Linux Local Security Checks	Local	high
329661	Linux Distros Unpatched Vulnerability : CVE-2026-59851	Nessus	Misc.	Local	high
329159	Fedora 44 : libssh (2026-0e46c91ccf)	Nessus	Fedora Local Security Checks	Local	high

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