Hi,

The following vulnerabilities were published for libssh.

CVE-2026-66032[0]:
| 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-2026-66033[1]:
| 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-2026-66034[2]:
| 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-2026-66035[3]:
| 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.


If you fix the vulnerabilities please also make sure to include the
CVE (Common Vulnerabilities & Exposures) ids in your changelog entry.

For further information see:

[0] https://security-tracker.debian.org/tracker/CVE-2026-66032
https://www.cve.org/CVERecord?id=CVE-2026-66032
[1] https://security-tracker.debian.org/tracker/CVE-2026-66033
https://www.cve.org/CVERecord?id=CVE-2026-66033
[2] https://security-tracker.debian.org/tracker/CVE-2026-66034
https://www.cve.org/CVERecord?id=CVE-2026-66034
[3] https://security-tracker.debian.org/tracker/CVE-2026-66035
https://www.cve.org/CVERecord?id=CVE-2026-66035

Regards,
Salvatore