A flaw was found in libssh. Logic errors in automatic certificate-based public key authentication can cause libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected by a server, leading to denial of service.

The remote Ubuntu 22.04 LTS / 24.04 LTS / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8699-1 advisory.

    It was discovered that libssh had a stack buffer overflow in its SFTP server when constructing directory     listing entries for long filenames. An attacker could possibly use this issue to cause libssh to crash or     execute arbitrary code. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-15370)

    It was discovered that libssh did not correctly handle SSH channel open messages advertising a zero     maximum packet size. An authenticated remote attacker could possibly use this issue to cause libssh to     consume excessive CPU resources, leading to a denial of service. (CVE-2026-59843)

    It was discovered that libssh did not correctly limit SFTP read request lengths in its server     implementation. An authenticated remote attacker could possibly use this issue to cause libssh to allocate     excessive memory, leading to a denial of service. This issue only affected Ubuntu 26.04 LTS.
    (CVE-2026-59844)

    It was discovered that libssh did not correctly handle ProxyCommand fork() failures. A local attacker     could possibly use this issue to cause a denial of service. (CVE-2026-59845)

    It was discovered that libssh did not correctly sanitize shell metacharacters when expanding usernames in     ProxyCommand strings. An attacker could possibly use this issue to obtain sensitive information.
    (CVE-2026-59846)

    It was discovered that libssh had incorrect AES-GCM tag verification when built with the OpenSSL backend.
    A machine-in-the-middle attacker could possibly use this issue to modify encrypted traffic without     detection. (CVE-2026-59847)

    It was discovered that libssh did not correctly handle SFTP server responses for unknown request IDs. An     attacker could possibly use this issue to cause libssh to use excessive memory, leading to a denial of     service. (CVE-2026-59848)

    It was discovered that libssh had logic errors in certificate-based authentication that could cause     clients to loop indefinitely when certificates were rejected. An attacker could possibly use this issue to     cause a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-59849)

    It was discovered that libssh could invoke data callbacks on channels after they had been closed. An     attacker could possibly use this issue to cause libssh to crash or execute arbitrary code.
    (CVE-2026-59850)

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.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - A flaw was found in libssh. Logic errors in automatic certificate-based public key authentication can
    cause libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected
    by a server, leading to denial of service. (CVE-2026-59849)

The Rocky Linux 10.2 host has packages installed that are affected by multiple vulnerabilities as referenced in the CIQ crlsa-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 CIQ 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 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 remote Debian 13 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-6410 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6410-1                   security@debian.org     https://www.debian.org/security/                     Salvatore Bonaccorso     August 02, 2026                       https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : libssh     CVE ID         : CVE-2026-0964 CVE-2026-0965 CVE-2026-0966 CVE-2026-0967                      CVE-2026-0968 CVE-2026-3731 CVE-2026-15370 CVE-2026-59843                      CVE-2026-59844 CVE-2026-59845 CVE-2026-59846 CVE-2026-59847                      CVE-2026-59848 CVE-2026-59849 CVE-2026-59850     Debian Bug     : 1127693 1142537

    Several vulnerabilities were discovered in libssh, a tiny C SSH library,     which may result in denial of service, information disclosure and     potentially the execution of arbitrary code.

    For the stable distribution (trixie), these problems have been fixed in     version 0.11.5-0+deb13u1.

    We recommend that you upgrade your libssh packages.

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

    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 SUSE Linux SLES16 / SLES_SAP16 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:22956-1 advisory.

    - CVE-2026-15370: stack buffer overflow in SFTP server longname construction (bsc#1272162).
    - CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
    - CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
    - CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
    - CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
    - CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
    - CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
    - CVE-2026-59849: denial of service via automatic certificate authentication loop (bsc#1272170).
    - CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

    Changes for libssh:

    - Update to 0.11.5:

     * Zero-initialize every ssh_string
     * Fix compatibility with C23 / gcc16
     * Fix multiple memory leaks, null checks, and error checks
     * Validate peer public key in DH key exchange
     * Avoid remote window overflow
     * Avoid off-by-one overflow during kbdint authentication
     * Avoid logging uninitialized sequence numbers
     * Avoid double conversion of SFTP version number
     * Send correct SFTP server version number
     * Avoid handling repeated SFTP INIT messages
     * Harmonize return values from SFTP server callbacks

    - Update %suse_version checks for SLES 16.x (jsc#PED-15815)

Tenable has extracted the preceding description block directly from the SUSE 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 openSUSE 16 host has packages installed that are affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21444-1 advisory.

    - CVE-2026-15370: stack buffer overflow in SFTP server longname construction (bsc#1272162).
    - CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
    - CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
    - CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
    - CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
    - CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
    - CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
    - CVE-2026-59849: denial of service via automatic certificate authentication loop (bsc#1272170).
    - CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

    Changes for libssh:

    - Update to 0.11.5:

     * Zero-initialize every ssh_string
     * Fix compatibility with C23 / gcc16
     * Fix multiple memory leaks, null checks, and error checks
     * Validate peer public key in DH key exchange
     * Avoid remote window overflow
     * Avoid off-by-one overflow during kbdint authentication
     * Avoid logging uninitialized sequence numbers
     * Avoid double conversion of SFTP version number
     * Send correct SFTP server version number
     * Avoid handling repeated SFTP INIT messages
     * Harmonize return values from SFTP server callbacks

    - Update %suse_version checks for SLES 16.x (jsc#PED-15815)

Tenable has extracted the preceding description block directly from the SUSE 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. Logic errors in automatic certificate-based public key authentication can     cause libssh clients to loop indefinitely when configured certificates are missing or repeatedly rejected     by a server, leading to denial of service. (CVE-2026-59849)

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

The remote Fedora 43 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-063caa9112 advisory.

    New upstream security release (#2503148)


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 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.

The version of libssh installed on the remote host is prior to 0.11.5 / 0.12.1. It is, therefore, affected by multiple vulnerabilities as referenced in the SSA:2026-202-01 advisory.

    New libssh packages are available for Slackware 15.0 and -current to fix security issues.

Tenable has extracted the preceding description block directly from the libssh 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
365394	Ubuntu 22.04 LTS / 24.04 LTS / 26.04 LTS : libssh vulnerabilities (USN-8699-1)	Nessus	Ubuntu Local Security Checks	Local	high
460583	Echo: libssh: security update to 0.12.0-3+e2	Tenable Cloud Security	Echo Local Security Checks	Local	high
460583	Echo: libssh: security update to 0.12.0-3+e2	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	high
354941	Rocky Linux 10.2 [CIQ] Security Update: libssh / libssh-config / libssh-debuginfo / libssh-debugsource / etc Multiple Vulnerabilities (crlsa-2026_55855)	Nessus	Rocky Linux Local Security Checks	Local	high
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
331648	Debian dsa-6410 : libssh-4 - security update	Nessus	Debian Local Security Checks	Local	medium
330564	SUSE SLES16 Security Update : libssh (SUSE-SU-2026:22956-1)	Nessus	SuSE Local Security Checks	Local	high
330077	openSUSE 16 Security Update : libssh (openSUSE-SU-2026:21444-1)	Nessus	SuSE Local Security Checks	Local	high
329584	Linux Distros Unpatched Vulnerability : CVE-2026-59849	Nessus	Misc.	Local	high
329166	Fedora 43 : libssh (2026-063caa9112)	Nessus	Fedora Local Security Checks	Local	high
329159	Fedora 44 : libssh (2026-0e46c91ccf)	Nessus	Fedora Local Security Checks	Local	high
328881	Slackware Linux 15.0 / current libssh Multiple Vulnerabilities (SSA:2026-202-01)	Nessus	Slackware Local Security Checks	Local	high

Detections

Analytics

CVE-2026-59849

high

Tenable Plugins

high

high

high

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high

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medium

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