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

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oracle CPUOct2026: MySQL Cluster >=8.0.0|<=8.0.38

oracle CPUOct2026: MySQL Cluster >=8.4.0|<=8.4.13

oracle CPUOct2026: MySQL Cluster >=8.0.0|<=8.0.50

oracle CPUOct2026: MySQL Cluster >=26.7.0|<=26.7.2

oracle CPUOct2026: MySQL Server >=8.4.0|<=8.4.13

oracle CPUOct2026: MySQL Server >=26.7.0|<=26.7.2

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There are packages installed that are affected by multiple vulnerabilities referenced in the following CVEs:

  - 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)

  - libssh2 through 1.11.1, fixed in commit 2dae302, contains an out-of-bounds heap read vulnerability in the
    sftp_symlink() function in src/sftp.c that allows a malicious SSH server or man-in-the-middle attacker to
    disclose heap memory contents or cause a crash by sending a crafted SSH_FXP_NAME response. Attackers can
    supply a link_len value larger than the actual packet data in SSH_FXP_NAME responses for SFTP READLINK and
    REALPATH operations, triggering a heap buffer over-read of up to target_len minus one bytes due to the
    missing validation of available packet buffer size before the memcpy operation. (CVE-2025-15661)

  - libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service
    vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause
    a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set
    nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over
    60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not
    apply to CPU-bound loops. (CVE-2026-55199)

  - libssh2 through 1.11.1 reads an attacker-controlled 32-bit attribute count from a publickey-subsystem
    response and uses it in the allocation num_attrs * sizeof(libssh2_publickey_attribute) without bounds
    checking, so on 32-bit platforms the multiplication overflows to an undersized buffer. A malicious SSH
    server can then drive the attribute-parsing loop to write past the allocation, causing a heap buffer
    overflow in a connecting libssh2 client. (CVE-2026-58050)

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

  - 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)

The remote host is affected by the vulnerability described in GLSA-202608-17 (libssh2: Multiple Vulnerabilities)

    Multiple vulnerabilities have been discovered in libssh2. Please review the CVE identifiers referenced     below for details.

Tenable has extracted the preceding description block directly from the Gentoo 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.

An update of the libssh2 package has been released.

The remote Fedora 43 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-eed9e67393 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 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.

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	Type	Severity
476436	Alpine: multiple libssh2 packages: security update to 1.11.1-r3	Tenable Cloud Security	Alpine Linux Local Security Checks	Local	critical
476436	Alpine: multiple libssh2 packages: security update to 1.11.1-r3	Tenable Self-Hosted Container Security	Alpine Linux Local Security Checks	Local	critical
458239	Echo: libssh2: security update to 1.11.1-1+e4	Tenable Cloud Security	Echo Local Security Checks	Local	critical
458239	Echo: libssh2: security update to 1.11.1-1+e4	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	critical
338224	GLSA-202608-17 : libssh2: Multiple Vulnerabilities	Nessus	Gentoo Local Security Checks	Local	critical
333651	Photon OS 5.0: Libssh2 PHSA-2026-5.0-92-0900	Nessus	PhotonOS Local Security Checks	Local	critical
332666	Photon OS 5.0: Libssh2 PHSA-2026-5.0-91-0900	Nessus	PhotonOS Local Security Checks	Local	critical
326401	Fedora 43 : libssh2 (2026-eed9e67393)	Nessus	Fedora Local Security Checks	Local	critical
325003	Ubuntu 24.04 LTS / 25.10 / 26.04 LTS : libssh2 vulnerabilities (USN-8486-1)	Nessus	Ubuntu Local Security Checks	Local	critical
324070	openSUSE 16 Security Update : libssh2_org (openSUSE-SU-2026:21057-1)	Nessus	SuSE Local Security Checks	Local	critical
323917	Photon OS 5.0: Libssh2 PHSA-2026-5.0-0900	Nessus	PhotonOS Local Security Checks	Local	critical
323626	Fedora 44 : libssh2 (2026-ca858b3ed8)	Nessus	Fedora Local Security Checks	Local	critical
323060	Debian dsa-6365 : libssh2-1-dev - security update	Nessus	Debian Local Security Checks	Local	critical
321726	Linux Distros Unpatched Vulnerability : CVE-2026-55200	Nessus	Misc.	Local	critical

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