libssh2 through 1.11.1, fixed in commit 7acf3df contains an out-of-bounds write vulnerability in ssh2_transport_read() that fails to enforce upper bounds on packet_length field. Remote attackers can send crafted SSH packets with excessively large packet_length values to corrupt heap memory and achieve remote code execution.

A public proof-of-concept exploit has been released and patches have not yet been released, but are expected soon

The remote Ubuntu 24.04 LTS / 25.10 / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8486-1 advisory.

    It was discovered that libssh2 incorrectly handled the sftp_symlink() function. A malicious SSH server or     machine-in-the-middle attacker could possibly use this issue to obtain sensitive information or cause a     denial of service. (CVE-2025-15661)

    It was discovered that libssh2 had a pre-authentication denial of service vulnerability in the     SSH_MSG_EXT_INFO handler. A malicious SSH server could possibly use this issue to cause a client CPU     exhaustion loop, resulting in a denial of service. (CVE-2026-55199)

    It was discovered that libssh2 incorrectly handled packet length fields. A remote attacker could possibly     use this issue to execute arbitrary code. This issue only affected Ubuntu 25.10 and Ubuntu 26.04 LTS.
    (CVE-2026-55200)

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 openSUSE 16 host has packages installed that are affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21057-1 advisory.

    This update for libssh2_org fixes the following issues

    - CVE-2026-55199: pre-Authentication DoS via SSH_MSG_EXT_INFO Handler (bsc#1268530).
    - CVE-2026-55200: out-of-Bounds write via Unchecked packet_length in transport.c (bsc#1268531).

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.

An update of the libssh2 package has been released.

The remote Fedora 44 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-ca858b3ed8 advisory.

    This update addresses a few security issues, one of which could plausibly result in remote code execution.


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 Debian 13 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-6365 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6365-1                   security@debian.org     https://www.debian.org/security/                       Moritz Muehlenhoff     June 25, 2026                         https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : libssh2     CVE ID         : CVE-2025-15661 CVE-2026-7598 CVE-2026-55199 CVE-2026-55200

    Multiple security vulnerabilities were discovered in libssh2, a     client-side C library implementing the SSH2 protocol which could result     in memory disclosure, denial of service or potentially the execution of     arbitrary code.

    For the stable distribution (trixie), these problems have been fixed in     version 1.11.1-1+deb13u1.

    We recommend that you upgrade your libssh2 packages.

    For the detailed security status of libssh2 please refer to     its security tracker page at:
    https://security-tracker.debian.org/tracker/libssh2

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

  - libssh2 through 1.11.1, fixed in commit 7acf3df contains an out-of-bounds write vulnerability in     ssh2_transport_read() that fails to enforce upper bounds on packet_length field. Remote attackers can send     crafted SSH packets with excessively large packet_length values to corrupt heap memory and achieve remote     code execution. (CVE-2026-55200)

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

ID	Name	Product	Family	Severity
325003	Ubuntu 24.04 LTS / 25.10 / 26.04 LTS : libssh2 vulnerabilities (USN-8486-1)	Nessus	Ubuntu Local Security Checks	critical
324070	openSUSE 16 Security Update : libssh2_org (openSUSE-SU-2026:21057-1)	Nessus	SuSE Local Security Checks	critical
323917	Photon OS 5.0: Libssh2 PHSA-2026-5.0-0900	Nessus	PhotonOS Local Security Checks	critical
323626	Fedora 44 : libssh2 (2026-ca858b3ed8)	Nessus	Fedora Local Security Checks	critical
323060	Debian dsa-6365 : libssh2-1-dev - security update	Nessus	Debian Local Security Checks	critical
321726	Linux Distros Unpatched Vulnerability : CVE-2026-55200	Nessus	Misc.	critical

Detections

Analytics

CVE-2026-55200

critical

Tenable Plugins

critical

critical

critical

critical

critical

critical