libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-2064 advisory.

    libgit2 Submodule path traversal (CVE-2026-53584)

    Unbounded Memory Allocation via Delta Object Result-Size Header (CVE-2026-53585)

    libgit2 version 1.9.4 and below is vulnerable to a heap out-of-bounds read in set_data() in     src/libgit2/transports/smart_pkt.c.

    The vulnerable code uses a fixed-size strncmp (smart_pkt.c:239) against the unvalidated capability buffer     of a smart-protocol pkt-line. When the bytes following the pkt-line in the contiguous receive buffer     happen to continue with ct-format=, the comparison spuriously matches, advancing format_str past the     pkt-line boundary. The following memchr(format_str, ' ', len - (format_str - line)) (smart_pkt.c:246) then     underflows its size_t size argument to ~SIZE_MAX and walks the heap looking for a space byte. An     unauthenticated remote attacker who controls (or man-in-the-middles) a Git server reached over     HTTP/HTTPS/SSH/git:// can trigger this on the FIRST ref-pkt of the refs advertisement, before any     capability negotiation has taken place. The OOB walk causes a process crash (SIGSEGV) when memchr enters     an unmapped page, and -- on heap layouts where memchr finds a stray space byte before crashing -- can     additionally drive the git_error_set(...'%.*s', format_len, format_str) formatter to copy a large window     of heap memory into the error string. (CVE-2026-53587)

    libssh2 through 1.11.1, fixed in commit 5e47761, contains a double-free vulnerability in the sftp_open()     function in src/sftp.c that allows a malicious SSH server to corrupt the heap of any authenticated client     opening an SFTP session. When a server responds to SSH_FXP_OPEN with SSH_FXP_STATUS containing FX_OK, the     response data buffer is freed, and if a subsequent sftp_packet_require() call returns a specific error     such as LIBSSH2_ERROR_CHANNEL_PACKET_EXCEEDED, the same pointer is freed a second time, enabling tcache     dup conditions on glibc systems that allow overlapping allocations and function pointer overwrites.
    (CVE-2026-66032)

    libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow     vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to     crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the     underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an     out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash     before any authentication occurs. (CVE-2026-66033)

    libssh2 through 1.11.1, fixed in commit a13bb6c, contains a missing bounds check vulnerability that allows     a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an     uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1     response parser reads a server-controlled comment_len value and advances the parse pointer without     verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from     adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup     path frees an uninitialized pointer from a non-zeroed realloc() region. (CVE-2026-66034)

    libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow     vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by     sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher     negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of     packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit     glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion,     overlapping live objects, and function pointer overwrite during the session handshake before     authentication. (CVE-2026-66035)

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 openSUSE 16 host has packages installed that are affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21549-1 advisory.

    - CVE-2025-15661: out-of-bounds heap read vulnerability in the `sftp_symlink()` function in `src/sftp.c`     (bsc#1268546).
    - CVE-2026-7598: integer overflow in function `userauth_password` of file `src/userauth.c` (bsc#1263890).
    - CVE-2026-58050: heap buffer overflow due to missing bounds check in attribute count of publickey-     subsystem response       (bsc#1269568).
    - CVE-2026-58051: uninitialized pointer freed when malformed responses are sent by an SSH server     (bsc#1269567).
    - CVE-2026-66032: arbitrary code execution via double-free in SFTP session (bsc#1272737).
    - CVE-2026-66033: denial of service via integer underflow in AES-GCM cipher negotiation (bsc#1272736).
    - CVE-2026-66034: information disclosure and potential arbitrary code execution via heap out-of-bounds     read       (bsc#1272735).
    - CVE-2026-66035: arbitrary code execution via heap buffer overflow during SSH negotiation (bsc#1272734).

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 SUSE Linux SLED15 / SLED_SAP15 / SLES15 / SLES_SAP15 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:3541-1 advisory.

    - CVE-2025-15661: out-of-bounds heap read vulnerability in the `sftp_symlink()` function in `src/sftp.c`     (bsc#1268546).
    - CVE-2026-7598: integer overflow in function `userauth_password` of file `src/userauth.c` (bsc#1263890).
    - CVE-2026-58050: heap buffer overflow due to missing bounds check in attribute count of publickey-     subsystem response       (bsc#1269568).
    - CVE-2026-58051: uninitialized pointer freed when malformed responses are sent by an SSH server     (bsc#1269567).
    - CVE-2026-66032: arbitrary code execution via double-free in SFTP session (bsc#1272737).
    - CVE-2026-66033: denial of service via integer underflow in AES-GCM cipher negotiation (bsc#1272736).
    - CVE-2026-66034: information disclosure and potential arbitrary code execution via heap out-of-bounds     read       (bsc#1272735).
    - CVE-2026-66035: arbitrary code execution via heap buffer overflow during SSH negotiation (bsc#1272734).

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 SUSE Linux SLES15 / SLES_SAP15 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:3526-1 advisory.

    - CVE-2025-15661: out-of-bounds heap read vulnerability in the `sftp_symlink()` function in `src/sftp.c`     (bsc#1268546).
    - CVE-2026-7598: integer overflow in function `userauth_password` of file `src/userauth.c` (bsc#1263890).
    - CVE-2026-58050: heap buffer overflow due to missing bounds check in attribute count of publickey-     subsystem response       (bsc#1269568).
    - CVE-2026-58051: uninitialized pointer freed when malformed responses are sent by an SSH server     (bsc#1269567).
    - CVE-2026-66032: arbitrary code execution via double-free in SFTP session (bsc#1272737).
    - CVE-2026-66033: denial of service via integer underflow in AES-GCM cipher negotiation (bsc#1272736).
    - CVE-2026-66034: information disclosure and potential arbitrary code execution via heap out-of-bounds     read       (bsc#1272735).
    - CVE-2026-66035: arbitrary code execution via heap buffer overflow during SSH negotiation (bsc#1272734).

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 SUSE Linux SLES12 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:3525-1 advisory.

    - CVE-2025-15661: out-of-bounds heap read vulnerability in the `sftp_symlink()` function in `src/sftp.c`     (bsc#1268546).
    - CVE-2026-7598: integer overflow in function `userauth_password` of file `src/userauth.c` (bsc#1263890).
    - CVE-2026-55199: pre-authentication DoS via the `SSH_MSG_EXT_INFO` handler (bsc#1268530).
    - CVE-2026-58050: heap buffer overflow due to missing bounds check in attribute count of publickey-     subsystem response       (bsc#1269568).
    - CVE-2026-58051: uninitialized pointer freed when malformed responses are sent by an SSH server     (bsc#1269567).
    - CVE-2026-66032: arbitrary code execution via double-free in SFTP session (bsc#1272737).
    - CVE-2026-66033: denial of service via integer underflow in AES-GCM cipher negotiation (bsc#1272736).
    - CVE-2026-66034: information disclosure and potential arbitrary code execution via heap out-of-bounds     read       (bsc#1272735).
    - CVE-2026-66035: arbitrary code execution via heap buffer overflow during SSH negotiation (bsc#1272734).

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 version of Tencent Linux installed on the remote TencentOS Server 4 host is prior to tested version. It is, therefore, affected by multiple vulnerabilities as referenced in the TSSA-2026:0785 advisory.

    Package updates are available for TencentOS Server 4 that fix the following vulnerabilities:

    CVE-2026-66035:
    libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow     vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by     sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher     negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of     packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit     glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion,     overlapping live objects, and function pointer overwrite during the session handshake before     authentication.

    CVE-2026-66034:
    libssh2 through 1.11.1, fixed in commit a13bb6c, contains a missing bounds check vulnerability that allows     a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an     uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1     response parser reads a server-controlled comment_len value and advances the parse pointer without     verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from     adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup     path frees an uninitialized pointer from a non-zeroed realloc() region.

    CVE-2026-66033:
    libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow     vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to     crash any connecting client by negotiating AES-GCM ciphers during handshake.

    CVE-2026-66032:
    libssh2 through 1.11.1 contains a double-free vulnerability in the sftp_open() function in src/sftp.c that     allows a malicious SSH server to corrupt the heap of any authenticated client opening an SFTP session.
    When a server responds to SSH_FXP_OPEN with SSH_FXP_STATUS containing FX_OK, the response data buffer is     freed, and if a subsequent sftp_packet_require() call returns a specific error such as     LIBSSH2_ERROR_CHANNEL_PACKET_EXCEEDED, the same pointer is freed a second time, enabling tcache dup     conditions on glibc systems.

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

  - libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow     vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to     crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the     underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an     out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash     before any authentication occurs. (CVE-2026-66033)

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

ID	Name	Product	Family	Type	Severity
337216	Amazon Linux 2023 : cargo-c (ALAS2023-2026-2064)	Nessus	Amazon Linux Local Security Checks	Local	high
335046	openSUSE 16 Security Update : libssh2_org (openSUSE-SU-2026:21549-1)	Nessus	SuSE Local Security Checks	Local	high
334785	SUSE SLED15 / SLES15 Security Update : libssh2_org (SUSE-SU-2026:3541-1)	Nessus	SuSE Local Security Checks	Local	high
333544	SUSE SLES15 Security Update : libssh2_org (SUSE-SU-2026:3526-1)	Nessus	SuSE Local Security Checks	Local	high
333542	SUSE SLES12 Security Update : libssh2_org (SUSE-SU-2026:3525-1)	Nessus	SuSE Local Security Checks	Local	high
333143	TencentOS Server 4: libssh2 (TSSA-2026:0785)	Nessus	Tencent Local Security Checks	Local	high
329627	Linux Distros Unpatched Vulnerability : CVE-2026-66033	Nessus	Misc.	Local	high

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