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EulerOS 2.0 SP15 : libssh2 (EulerOS-SA-2026-3921)

high Nessus Plugin ID 364083

Synopsis

The remote EulerOS host is missing multiple security updates.

Description

According to the versions of the libssh2 packages installed, the EulerOS installation on the remote host is affected by the following vulnerabilities :

 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)

 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 grows its publickey list with SSH2_REALLOC but does not zero-initialize new entries before parsing populates them, so a parse failure reaching the cleanup path leaves libssh2_publickey_list_free operating on an uninitialized entry. A malicious SSH server offering the publickey subsystem can use a malformed response to make cleanup free an uninitialized, attacker- influenceable attrs pointer in a connecting libssh2 client.(CVE-2026-58051)

 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 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 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 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, 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 EulerOS libssh2 security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Update the affected libssh2 packages.

See Also

http://www.nessus.org/u?aea0850b

Plugin Details

Severity: High

ID: 364083

File Name: EulerOS_SA-2026-3921.nasl

Version: 1.1

Type: Local

Published: 10/8/2026

Updated: 10/8/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: High

Score: 7.6

Percentile: 98.26

CVSS v2

Risk Factor: Medium

Base Score: 6.1

Temporal Score: 4.8

Vector: CVSS2#AV:N/AC:H/Au:N/C:P/I:N/A:C

CVSS Score Source: CVE-2025-15661

CVSS v3

Risk Factor: Medium

Base Score: 6.5

Temporal Score: 5.9

Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

CVSS v4

Risk Factor: High

Base Score: 8.7

Threat Score: 7.7

Threat Vector: CVSS:4.0/E:P

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS Score Source: CVE-2026-66033

Vulnerability Information

CPE: cpe:/o:huawei:euleros:2.0, p-cpe:/a:huawei:euleros:libssh2-devel, p-cpe:/a:huawei:euleros:libssh2-help, p-cpe:/a:huawei:euleros:libssh2

Required KB Items: Host/local_checks_enabled, Host/cpu, Host/EulerOS/release, Host/EulerOS/rpm-list, Host/EulerOS/sp

Excluded KB Items: Host/EulerOS/uvp_version

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 10/8/2026

Vulnerability Publication Date: 6/17/2026

Reference Information

CVE: CVE-2025-15661, CVE-2026-55199, CVE-2026-58050, CVE-2026-58051, CVE-2026-66032, CVE-2026-66033, CVE-2026-66034, CVE-2026-66035

IAVA: 2026-A-0788