CVE-2025-15661

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.

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.

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.

libssh2 is a library implementing the SSH2 protocol as defined by Internet Drafts: SECSH-TRANS(22), SECSH-USERAUTH(25), SECSH-CONNECTION(23), SECSH-ARCH(20), SECSH-FILEXFER(06)*, SECSH-DHGEX(04), and SECSH-NUMBERS(10).

Security Fix(es):

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 is a library implementing the SSH2 protocol as defined by Internet Drafts: SECSH-TRANS(22), SECSH-USERAUTH(25), SECSH-CONNECTION(23), SECSH-ARCH(20), SECSH-FILEXFER(06)*, SECSH-DHGEX(04), and SECSH-NUMBERS(10).

Security Fix(es):

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 is a library implementing the SSH2 protocol as defined by Internet Drafts: SECSH-TRANS(22), SECSH-USERAUTH(25), SECSH-CONNECTION(23), SECSH-ARCH(20), SECSH-FILEXFER(06)*, SECSH-DHGEX(04), and SECSH-NUMBERS(10).

Security Fix(es):

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 is a library implementing the SSH2 protocol as defined by Internet Drafts: SECSH-TRANS(22), SECSH-USERAUTH(25), SECSH-CONNECTION(23), SECSH-ARCH(20), SECSH-FILEXFER(06)*, SECSH-DHGEX(04), and SECSH-NUMBERS(10).

Security Fix(es):

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 is a library implementing the SSH2 protocol as defined by Internet Drafts: SECSH-TRANS(22), SECSH-USERAUTH(25), SECSH-CONNECTION(23), SECSH-ARCH(20), SECSH-FILEXFER(06)*, SECSH-DHGEX(04), and SECSH-NUMBERS(10).

Security Fix(es):

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 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 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)

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.

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.

• SECURITY UPDATE: out-of-bounds heap read in SFTP symlink handling
  • debian/patches/CVE-2025-15661.patch: validate that the link length in a SSH_FXP_NAME response fits within the received packet before copying it in sftp_symlink() in src/sftp.c
  • CVE-2025-15661

The updated packages fix security vulnerabilities: Heap Buffer Over-read via sftp_symlink() in sftp.c. (CVE-2025-15661) libssh2 userauth.c userauth_password integer overflow. (CVE-2026-7598) Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler. (CVE-2026-55199) Out-of-Bounds Write via Unchecked packet_length in transport.c. (CVE-2026-55200) Integer Overflow in publickey Subsystem Attribute Allocation. (CVE-2026-58050) Free of Uninitialized Pointer in publickey List Cleanup. (CVE-2026-58051)

These are all security issues fixed in the libssh2-1-1.11.1-3.1 package on the GA media of openSUSE Tumbleweed.

This update for libssh2_org fixes the following issues:

• 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).

Root has patched CVE-2025-15661 in the libssh2 package for Root:Debian:11. Multiple fixed versions available.

Root has patched CVE-2025-15661 in the libssh2 package for Root:Debian:12. Multiple fixed versions available.

This update for libssh2_org fixes the following issues:

• 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).

This update for libssh2_org fixes the following issues:

• 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).

This update for libssh2_org fixes the following issues:

• 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).

This update for libssh2_org fixes the following issues:

• 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).

This update for libssh2_org fixes the following issues:

Security issues fixed:

• 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).

Other updates and bugfixes:

• Fix an issue with Encrypt-then-MAC family (bsc#1221622).
  • Test the ETM feature in the remote end's configuration when receiving data. Upstream issue: #1331.
• Always add the KEX pseudo-methods ext-info-c and [email protected] when configuring custom method list (bsc#1218971).
  • The strict-kex extension is announced in the list of available KEX methods. However, when the default KEX method list is modified or replaced, the extension is not added back automatically.

This update for libssh2_org fixes the following issues:

• 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).

This update for libssh2_org fixes the following issues:

• 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).

This update for libssh2_org fixes the following issues:

• 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).

This update for libssh2_org fixes the following issues:

• 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: attacker controlled attribute count from a publickey-subsystem response is used without bounds checking and can cause to a heap buffer overflow in a connecting libssh2 client (bsc#1269568).
• CVE-2026-58051: public key list is increased and does not zero-initialized new entries, which can cause an uninitialized pointer to be freed when a malformed response is 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).

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)